I was in the Pub recently and someone asked me why there was no Player Character versus Player Character combat allowed <PC vs PC or playerkilling>. I responded that it was decided from the beginning that the Kingdom of Drakkar would not allow PC vs PC combat and that it was the best decision we had made. The person responded with "Would you care to 'defend' that 'best decision? I had not thought it was needed but since they asked I'll address this issue as one who both works and plays in an online service.
In this genre, the online industry's goal is to create an ongoing RPG 'persistent world' where you can enter and leave at any time, grow your character, meet friends, go on quests, do battle, etc. Games such as Ultima Online, the Kingdom of Drakkar and others expect more people online for longer periods of time. Folks will play a stand-alone title for a few weeks; they may frequent some online services that feature pkilling for several months. The online connection to other people makes it satisfying for an extended period. In the persistent world games, this 'extended period' is considered in years of play, not just months. In an online role-playing world, some rules of conduct go a long way toward turning a world from complete anarchy to a place where friends meet to play and have fun. Character development is the whole point of a game like this. Why make it possible for one segment of your user base to alienate another segment by allowing unlimited PKilling?
The popular argument by pro-pkillers, people who are usually pkillers themselves, says that it is no different to be killed by another player than it is to be killed by a creature in the game. I can tell you from personal, bitter experience, that it is very different. In the course of my work I hear the problem calls and the cancellations of newbies beset by difficulties in games, especially that caused by other players. Newbies DO quit because of dieing, and *more often* if they are slain by PCs than if by monsters. The fact that another player can trash your character that you've been working hard to build, that the player can pick and choose the time to hurt you, that the pkiller can choose when to initiate the fight, when to break it off and that he can almost always avoid any penalty for it makes matters worse. Monsters do not laugh and insult you when they see you later in the game or conference room. Monsters do not exit the game to avoid retaliation. Monsters do not reroll to avoid retaliation. Monsters have to face their foes on more even terms than Pkillers. Personally, I like to play games with monsters in them, I avoid games with *rampant* Pkillers in them. Rules of conduct are a good thing. An online RPG is NOT capable of sustaining the freedom of action of Real Life <tm>. There probably is a place for PC versus PC combat if it can be kept within the role-playing aspects of the game. The thing about Pkilling is that it is not done in a role-playing sense unless the players are all role-playing psychopaths. There are NO inherent repercussions that keep an online society from self-destructing as Diablo did.
A game with *absolutely no chance* for PCs to interact hostilely would lack a certain edge, but a game with Rules of Conduct is far from what some pkill advocates call a 'chat room'. During travel between towns, there are many hostile and non-hostile computer-run creatures. This provides the depth that many pkill games are lacking even when there are many Player Characters around. Providing a magical world of adventure without forcing everyone into the 'fight or flight' mode of unbridled Pkilling is essential.
Players of online games with rules against Pkilling have fun exploring, meeting companions, developing their characters, facing challenges, completing quests and ridding the world of evil minions. The last thing they want is to have a character they've worked very hard to build be jumped and trashed one day by a pkiller who thinks THIS IS WHAT ROLE-PLAYING IS ALL ABOUT!