Not only that, they will have wives, girlfriends, and children; they may eventually have employees. You can not stop them period. They are a part of the human population. They can not be weeded out.
Peers who condone bullying are probably being manipulated into doing so, by someone with narcissistic traits who is skilled at whipping up hate towards the intended victims. It's not a normal attitude at all, it's very much a red flag that something quite nasty is going on.
I would alternatively suggest to make the punishment severe and make sure bullies can't get away with it.