Case study: You are a part of a game, say 'Mafia', if you know how it is played. Here, a moderator selects a 'Mafia' and a 'God'. The Mafia can kill anyone, the God can save anyone. All happens under the strict moderation of the moderator and everyone is supposed to keep their eyes closed. At the end a voting is done by the participants to find out who might be the Mafia among them. Since the Mafia has the power to kill anyone, naturally the team wants to kill the Mafia.
Question: When you cast votes to find out the Mafia, what's the correct usage - 'vote for the Mafia' or 'vote against the Mafia'?
Key point here might be the fact that the Mafia is someone you are trying to find out and hold as the convict. It's the negative character here.