The fact that you share a common enemy does not make you allies.
Walk into a room with 10 strangers and smack each of them in the mouth on your way by.
All of a sudden 10 strangers who don't know each other and have nothing in common (other than the smack in the mouth that you just gave them) have a common goal.
Are ANY of them in the wrong for wanting to return your smack in the mouth?