I mean, it all depends on the group of guys. Peer pressure can be good. I can say that I'm confident that there were a number of hayseedy quasi-racisty guys that entered DU who dropped those ideas/habits extremely quickly due to positive influences and exposure to real life minorities in our house.
I think that if there's a bunch of dumbass racists all living under one roof together, then yeah, it's going to continue to breed dumbass racist culture. But if there's enough smart, well liked dudes with decent world-views, then frats can be a breeding ground for positive influences. Maybe that's idealistic, but I can say that I think I'm a better/more well rounded dude than I would've been had I not joined.