Ryan Shwayder has a look up at what he calls "MMOrality"
-- the idea of a calling within any given game that determines how we as our avatars act. When newbie players first sign on to a new game, they are innocent in every meaning of the word-- they have no idea how to act, and even though they may do things that are against the ingame code (killstealing, ninja looting, grabbing quests without grouping, and so on), they are innocent, because they don't know yet what's right and wrong. Only after they're introduced to the "MMOrality" within the game can they figure out whether they want to be immoral, and go against the codes put in place by the game, or moral, and follow the etiquette and standards laid out by the other players.
It's an interesting thought, and not a new one
-- just as we have morality in the real world, our virtual worlds also have their own codes that can be upheld or broken. Shwayder speculates, however, that this morality requires PvP-- players can only uphold the morality they've put in place if they have the option to control other players by ganking them. But I'm not so sure that's true.
There are definitely ways to define behavior in a PvE environment-- guilds are one way these rules are passed around. Each guild has their own rules, and if those rules are broken, guilds (and even their allies) can blacklist players or punish them by not allowing them to enter into group raids and other places where the best rewards can be found.
Every society, real or virtual, has their own set of codes to live by, and it's very interesting to see how these are propagated in a virtual world. Whether via PvE grouping, or PvP retribution, every game has its own set of MMOrality that new players have to be taught in order to thrive and flourish socially in the world their characters live in.