Not to defend racism, but you'll find that pretty much every race that's not 2D gets shit on when you're on 4chan. That's just part of being a moderator-lite website. The entire idea is you shouldn't bring your real life onto the site, you'll find people ready and able to tear down anything for incredibly inane reasons. Why is it that it's so prevalent is an excellent question; why do people resort to such strong racist/sexist/divisive opinions when they get to have a mask?