The CoC isn't for them. As you mentioned, they're gonna be assholes no matter what. Kicking someone out of a group is possibly traumnatic but usually a bunch of drama. Having the god king of the group capriciously kick random people out of the group for no clear reason, and without communication as to why leaves the remaining members worried they could be next. I mean, sure, if you want to be the groups dictator and rule by fear, I guess that's fine, but imo that's no way to run things. By having something documented, with a procedure, gives a framework to follow for when you do have to kick someone out that's a bit less made up than "we just didn't like that person".