What's your attitude towards PVP?

[Yora]

My campaigns all require that all PCs generally like each other and want to work together. That's really the only requirement I make other than the available race and class options for the setting. Otherwise it makes no sense for a PC to be in the party and why would the other keep dragging him around?

If players think they have good reason to turn on another PC, that's fine with me. But the last word is always with the player whose character is being targeted. That's the one instance where anyone has a say on what someone else's character is doing. The character can still want to turn on another PC, but if that player decides that he's not going through with it, that's it.

I had one case in which a player wanted to pick a magic item from another player's pack, but since I got a note that the character is only going to study it while the other sleep and then put it back, I went through with it without asking the player who had taken the item for safekeeping, specifically to make sure the other character isn't fiddling with it.
The player was going against the specific agreement of the rest of the party that the magic item should be left alone, who even took steps to keep that one character's hands away from it. That's a player causing conflict with the rest of the party, but since it didn't mess with anyone else's characters, I saw no reason to stop it. The fallout of it is for the players to work out.

 

[pemerton]

Totally agree. It’s not typically what I like doing, but it’s very common and popular. If I were playing in such a game, I’d approach creating and playing my character differently than I would other games.

Absolutely, on both points (popularity; it what is involved in playing in such a game).

 

[AbdulAlhazred]

Maybe.

But consider this as a premise: a group of bitter adventurers get together and, while drowning their sorrows in a tavern one night, collectively decide "Screw it. We're gonna band together as friends and allies; we'll cover each other's backs, but the rest of the world can go eff itself and we're gonna help it along with that by any means possible."

And so they start raiding and looting and pillaging and butchering...all the usual Evil stuff, only they look out for each other and actually keep their promises to cover each others' backs.

Boom - instant long-lasting Evil campaign premise. And little if any reason for PvP.

I would say if there's enough verisimilitude in characterization to engage me, then these guys will need to invent a 'myth', an ideology, which makes them the good guys. While others may see them as evil, this kind of group will not see ITSELF as evil. They might go so far as to acknowledge that they "do some evil things" in service to whatever cause they've invented to justify their actions, and leadership might be seen as "brutal but on our side" etc. You can see this sort of thing in action, and it could be modeled by players in an RPG. Of course the main pattern that emerges is that eventually the whole thing devolves into some sort of cult of personality or something similar, and then down some rabbit hole or other. You can GET to basically stark raving evil that way, but none of these people will label THEMSELVES as evil, or if they do it will come as some terrible revelation, usually followed by separating from said group.

My bet is that your scenario is basically like the genesis of gangs. A group of people, living in an 'outsider' role in society band together and create some sort of gang. Again, they will take on some level of ideology, symbolism, and construct a gang culture which distinguishes them from society as a whole. In all the cases I know of these gangs are seen as an in-group, sort of like a family, that they owe loyalty to and to which they attribute positive attributes, including the attribute of opposition to the out-group, the rest of society. They may take this to the level of basically labeling everyone else as "not human" or something like that. I can't draw examples from RL here, but you can clearly look around and see how this works. Again, they never see themselves as EVIL.