Because they don't care about the rules, but they know the other side does. Whenever they act, they defend not their actions, but the process by which they were allowed to do them. If fascists break the rules, liberals can only request that the rules be followed. If they follow the rules, put on a tie and speak like an academic, liberals can only trust that their ideas will be voted against. In either case, they don't know how to call a fascist a fascist, and they don't know how to fight fascism within the current ruleset, and they never will.