On the game I staff on we've outright banned antagonist characters -- but that doesn't mean everyone needs to sit and hold hands around the campfire. Our theme technically makes it possible to bring in very antagonistic groups such as the Spanish Inquisition or WWII Nazis (the literal examples used) and we don't want those.
Why? Because we are telling the story of a group of people in a situation, and how they manage to survive in that situation. If they end up murdering each other in back alleys instead of taking on the game's antagonists, it's going to be a short and miserable story.
That, however, does not mean that people aren't allowed to antagonise each other. Want to play someone with miserable social skills or for that matter, a manipulative asshole? Fine by us as long as you realise that any consequences of your IC behaviour are also for you to deal with. People aren't always nice. People aren't always capable of getting along. People are sometimes dicks.
The key issue -- to my eyes as a game designer -- is what kind of antagonism the game 'officially' sanctions. If you have factions like the example above, of Camarilla and Sabbat, then members of those are going to be in opposition to one another. If you don't have factions or everyone is a part of the same faction, then some people are still going to be in opposition to each other simply because they don't share views or just plain don't get along. This is fine.
The trick is to avoid indirectly sanctioning OOC dickish behaviour. You don't want the kind of 4chan edgelord who comes onto a game with the single purpose of antagonising everyone else in the name of freedom of speech and lol get a sense of humour.
This is why we run PVE, not PVP. Too old, too tired, too jaded to deal with more of those. Which, again, does not mean that we prohibit people from being dicks IC -- we just don't give them a shield to hide behind when their dickery has consequences from other players.
