My personal comments are in italic. I have attempted to apply some logical order to the discussion. There's several original articles missing that I apparently did not save, or moved to a different discussion. My appologies if the resulting summary looks somewhat fragmented.

This is one of the subjects that never fail to spark heated discussion on any newsgroup or maillist about muds. This is a summary of the most common arguments, not a position in that discussion. In case anybody is interested I am personally opposed to PK in any form but I try not to let it show in this summary. I hope I have succeeded.
Marian

For those unfamiliar with the term PK is short for Player Killing. Or the act of one player attacking another. There is also player stealing (one player stealing gold or posessions from another) but for this summary I have treated this as basically the same behaviour. Many games allow this in one form or another. Some have no restrictions, other only allow it under specific circumstances, e.g. players must register their interest in pk by joining certain clans or alignments, or limit pk to certain rooms or areas within the game. Yet other games allow pk but have powerful law enforcers hunt down such killers. And some games make every effort to make pk impossible. Whatever the policy regarding pk, every game will have its regular debates among the players about the subject.

The biggest reason I see why this is such a volatile subject is because it borders on harassment, at least in the mind of some players. Attacking another player comes close to a personal attack. It frequently is interpreted as such by the victim. It also is frequently used in that way. Because so many players interpret it that way pk is a subject that is very volatile and requires carefull attention by the administration of any game.
Marian

Matt Chatterley started this by asking a couple of questions. The following discussion (of which only a part of the posts are used here) touched on the subject on the perception of PK by the victim and on ways to enforce no PK rules within the game. The second subject inspired other threads later.

Matt Chatterley
1- Is it possible to get players to treat death from another player differently to death from a monster, or NPC of some sort, that attacked them in a similar manner?

This introduces the common argument of reasonable behaviour. This is an emotional argument and as such hard to refute

Marian Griffith
Many players will be mildly upset when they're attacked for no reason by another player. In fact, the standard excuse for PK on many muds is that it allows players to take revenge for being attacked by others.

Matt Chatterley
Hmm, I think you're right on the last - and also the first now I think. You're not going to automatically connect that Fred is hitting you because you stole his bread a while ago. You might of course, then it's more excusable. As a side note: it should be possible to attack and fight with things, without killing them, and this is also going to be available for a player to teach another player a "lesson" without a sharp point.

(Marian Griffith)
There are many players who will not see any difference between being killed by a player or being killed by a monster. Others, like me, won't feel it is the same. As long as you provide meaningfull reasons to fights (and thereby ways to avoid those fights!) it is not so bad. What particularly rankles is being attacked for no apparent (or valid) reason.

Matt Chatterley
Yeah. The inherent problem here of course, is many players attack NPCs for no reason at all, and the same to other players. Things would be different if you are to be equally reprimanded for killing an NPC or player in a town, and not at all outside (unless they or their guild come after you in retribution). Guild behaviour will be encouraged (ie: Fred killed John, are we gonna let him get away with that?!).

This uses the argument of revenge as a reason for allowing pk. While probably valid it is also, in part, a circular argument. Being attacked and killed by other players is one of the reasons to allow players to attack and kill others.

Adam Wiggings
Yes. Well, of course, they aren't attacking characters (PC or NPC) for no reason, they are attacking them in order to get money, experience, and equipment. Take away this motivation, make combat extremely chancey, and suddenly there's much less reason to attack other people. On top of this, make the characters be more interested in the world around them by giving them actual political and/or social tie-ins.

Here is touched on the subject that in games that focus entirely on combat players are likely to deal with anything by fighting it. It also addresses in a round-about way the issue of reasons for being attacked.

Make it so that the hometown for the player's race really is a home to them. Some place they can always go for food, healing, repairs, safety among their fellows, etc etc. If you attack members of your own race (player or npc), you're branded an outcast and tossed out into the big bad world with no more help from that quarter.

Other things along this line: allow players to own shops and taverns in town. If someone knocks over the shop, then they have an actual player to reckon with.If someone aids the shopkeeper when someone else is attacking it, have the shopkeeper remember their name and relay it to the PC when she returns. Now there's a real motivation to help out NPCs who aren't even of your same race or have any special relation to you.

(Matt Chatterley)
2- I fully intend to permit PK (and treat it as near to killing NPCs as possible). For instance, attacking anything in a town (except invaders) will be considered a crime - obviously less serious if it's a creature of some kind, but a shopkeeper would be treated the same as another player.

Marian did not respond to the original question here. The subject of law enforcement is sufficiently interesting that it draws a lot of discussion on its own. Also the topic raised by Matt here is discussed in depth in other threads.

Marian Griffith
Most towns would have a law to forbid carrying weapons openly. Unless you are a guard or a -very- noble visitor or inhabitant. The amount of damage you can do with a simple eating knife is far less. And those fights are easier to break up for the guards.

Matt Chatterley
Absolutely. Weapons are to be sheathed (possibly simply represented by unwielded), or put away upon entry, and being caught with a weapon openly in view is a punishable offence.

Adam Wiggins
The trick is to be careful with this. I've seen this implemented plenty of times but never well. The main problem is that you often end up doing this:
] kill gatekeeper
You start thumping on the gatekeeper with your fists.
] draw sword
You draw your sword.
You slash the gatekeeper, who dies from the blow.
] open gate
But your hands are full with your sword!
] growl
You growl.
] sheathe sword
You sheathe your sword.
] open gate
You open the gate.

(Matt Chatterley)
Dodgy characters (if you've been in trouble here before) may well be asked to surrender weapons at the gates.

Adam Wiggins
You could have a number of different towns, which range from completely lawless outposts where you can do what you please to highly fortified cities which allow no weapons whatsoever within their gates. The later is more hassle, but if you want to go about your business without fearing that some ruffian is going to cut you down in hopes that you have a few coppers in your purse, it's kind of nice.

Another important issue is touched here: Give players a certain degree of control over the risks they want to take. Part of the thing that annoys people about pk is the apparent unfairness of it. A player can not usually avoid being attacked in the way they can avoid dangerous areas.

Other ideas: only citizens can carry weapons, and then only those that are registered. Restrictions on types of weapons (for instance, no blades) or areas of the town where you can go with them. And so forth - there's no reason at all that it should be the same in every town.

(Matt Chatterley)
In responding to an armed conflict, guards will not worry about applying lethal force. In an unarmed conflict, they'll be friendlier, and join in to break it up. Or relatively unarmed, anyway.

Adam Wiggins
Yeah. I've always wanted to be able to get into fistfights in bars or other less intense combat situations, but in general there is no particular distinction between lethal and non-lethal combat.

Jeff raises the issue of players who try to harm others rather than play a game. This is one of the problems that get tangled in the general discussion whether or not pk should be allowed in a game.

Jeff Kesselman
There is a social problem in players purposely trying to hurt other players by killing their characters for no good RP reason at all.

Chris Lawrence
If you don't consider the violation of true RP a problem, then this is less of a problem. If you're not attempting to run (or enforce) a solely immersive RP game, then I can see little reason to get upset at the for no good RP reason at all.

Marian introduces the concept of cooperative play. This is something not everybody else agrees on but it seems to be part of at least some of the roleplaying games

Marian Griffith
The problem of obnoxious players can't be easily brushed aside. There are some people who don't want to play at all but try to gain power over other players. The classical example of a bully.
Roleplaying assumes a certain cooperative attitude of the players. Even if somebody wants to rp an evil or selfish personality this should still be coordinated with the others.
You have to do something about those players who don't want to play even by this minimum of courtesy. Or worse, who enjoy upsetting others for the power it gives over their emotions. Allowing such characters to be killed in the game is not a definitive solution.
There are some players who don't want to play the game. Bartle, in his article for the journal of mud research, qualifies them as people who want to gain control. This may be control over the game, but it may also be control over other players.

[Ling says that he has at times killed everybody on a mud. Using the RP argument when needed. He continues to point out that without dangers the game can be too easy to win]

Marian points out that for Ling the pk may have been fun but she wonders if the same is true for his victims.

Marian Griffith
Perhaps a game should not be about winning but aboutplaying. There should be real, and perceived, danger in such game but the goals ought to be defined by the players, not by the game.
Perhaps pk is to be allowed, if it fits in the context of the game world and is not the focus of the game. High ranking players may hire assassins to eliminate rivals. Low level players should be safe from such tactics. How this can be enforced by a game is another question though.

(Jeff Kesselman)
ONE suggestion is to have you NEVER go below unconcious by damage done by another player... only monsters can outright kill you.

Chris points out here what most people feel about pk. It causes a direct and personal effect. This is the strength and root of the problem about pk.

Chris Lawrence
Part of the player-value in PK is the awareness that the killer caused a real and direct effect on another human. Making the effect death gives a certain permanence to the effect. Making it merely unconciousness (and probably the loss of various EQ etc) would seem to encourage "baiting" (repeated taunting of a player by a PK'er who keeps on knocking them unconcious).

A key contribution. It explores the way how certain players will (ab)use the ability to kill others for reasons that have nothing to do with the game.

Marian Griffith
This is indeed the strength and the great weakness of allowing players to fight each other. The problem is that if 'death' is expensive disruptive players win because they don't care for their characters other than as a way to (involuntarily) affect other players (i.e. upset them). And if 'death' is cheap they still win because they can claim that the victim doesn't loose much (which in game mechanics may be true, but in emotional effects isn't).

A parallel thread that ties in with the subject being discussed.

Adam Wiggins
Some folks want to play a mud where it is impossible to hurt other players; is this possible to achieve in any sort of semi-complex or consistant game world?

John Lambert
In a complex world there are more ways to harm other players, directly or indirectly

Marian Griffith
In my thinking PK is not a problem with abilities but with mentality. That means the prevention should be handled through administration rather than through the code. A game mechanic that makes fighting other players dangerous is not going to deter unstable or plain obnoxious players.

Maddy
The easiest solution I can think of, is to just make it almost impossible for this type of person to work out who are other players. If they can't get a list of who is on, then how can they know that Bubba is a player and hence that they'd want to kill him?

(Jon Lambert)
PK could be more or less lethal in a safe area, and the result of this removes you from the game for some time. This way players will have to actually play after the kill to get back into the game.

Matt Chatterley
Points out that if players are likely to be removed from the game for killing and must spend time and effort to return to the gameplay this will make people consider if they want to take that risk. Obnoxious players likely will not bother to try and leave.

Marian Griffith
Deterring players from killing is not going to stop everybody. Some will create a new one. Short of sitebanning nothing is going to stop them.

Matt Chatterley
Preventing players from creating several characters is easy if players need administrator approval.

Maddy introduces a common argument. Roleplaying evil characters requires players to behave evilly. This argument is entirely true. The only problem that I see with it is that some people are hiding behind this argument when they are, in fact, doing something else entirely.

Maddy
Sitebanning is not a definitive answer either. Some players try to achieve that.
It also may not be possible to distinguish between a real jerk and a role-played jerk.

Example of unfairness as a reason to reject pk. Similar discussions can be found in the Lambda moo case

Caliban Darlock
A player I know decided it might be cool to play a six year old. Just a regular everyday six year old. She was having great fun with it for about six months; it opened a lot of RP possibilities for herself and others.
The problem is, she ran into a character whose character background and concept indicated that he was a child molester. Entirely in keeping with his character, he kidnapped, molested, and killed her character. Just because she was a child. He managed to get into the same area with her on a deserted street, and called a staff member saying he was kidnapping the child by knocking her over the head. He then simply dragged her off and said 'Okay, I'm basically going to kill you, and there's nothing you can do about it'. This was true. Logically, she had no options. He was rather expert at it, after all. But the player -- in fact, a LOT of players -- were up in arms about this. His argument was that this is what his character would do. The staff supported this by saying that unfortunately, he was completely in character and completely justified within his character concept and the abilities available to him.
Now, the question that I have is, was that really fair? Did she have a right to be upset? I certainly think she did. My argument is that he should NOT have killed the character; his argument was that she could have identified him. This is true. However, why in a world theoretically full of children that are NOT being played by participants in the game did he have to do this to a player character? Should the player just go 'oh well' about the loss of a character she had played for six months, just because she happened to run into someone who could come up with an excuse to off her?

Marian Griffith
What was really wrong of this player's part is that he involved another player in a plot without in the least attempting to figure out how she felt about the whole situation. This is where a roleplaying game should still be a game. All involved must have fun. While it may be in-character it wasn't much fun for the victim. This is why many rp games havea warning against developing plotlines that may seriously harm the characters of other players without them basically agreeing to the plot.

(Caliban Darlock)
Some other players hunted him down and killed his character in response.

Marian Griffith
There is no real difference between what this player did to his victim and what was done to him. His own roleplaying was unjustified even if it was in line with his character.

This thread explores the nature of story telling and the impact pk has on that.

Marian Griffith
For some players roleplaying is about telling a story through their characters. If somebody single sided decides to kill that character they force the story to end before there was a chance to fully explore that story.

Adam Wiggins
But who is going to decide when the story is finished?

Marian Griffith
Characters in roleplaying games do dangerous things and may be killed. The problem is if somebody else kills them without your consent. There is no clear answer to whether this is allowed or not.

[responding to Adam who points out that Sometimes you make your character do things that are lethal so the others can continue.]
As long as it is yourself who decides what to do there is no problem here. Only if somebody else takes control over your character and causes their death.