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.

It’s very common and very natural. We all try to find our in- and by extension, out-group.

Narcissists just make the problem much, much worse.