I was wondering if it's absolutly necessary, to add rules or constraint to prevent player from playing with a bad attitude.
-Like rules to prevent "grouping against a player"
-Give disavantage or some kind of point loss to a player who always use actions that causes damage to other players strategy in a game
-Give bonuses to a player that was attacked a lot by the other player.
etc.
All these rules has one meaning, to help the pacific player and to try to stop agressive attacking players.
Is it really necessary?
I would personally shy away from these kinds of rules. I don't play that way, but some people find it fun (even the victims, because they could be the screwers later on). If such behavior breaks the game, then you need to look at balance. If the solution is to make rules against that kind of behavior, then work it into the game or theme. Make sure there is a reason for why ganging up, etc, is punished, rather than just "don't play that way."
Take a look at Steve Jackson's Munchkin. Ganging up against people is a big part of that game and there are both advantages and disadvantages to ganging up both for and against other players. It really adds to the gameplay in this case, but also provides some insight into how to moderate it.