I love how anonymity engenders such honest commentary. When people aren't tied down to their reputation/ego, they are free to say what they really think.
Is it really honest? Anonymous discussion tends to bring out the bigots - there's even some of it in the linked thread - but is it their genuine opinion, or could it be that it's just bored teenagers trying to rile someone up for a laugh?
I see this kind of "shock" throughout the techy mainstreamy politcally correct communities. It seems to me that the people that take issue with bigotry are themselves somehow weak through some kind of insecurity manifesting itself as a desire to fix this perceived "injustice". Because, you know, muh feels.
4chan just doesn't care about your feels. It's funny to say this (see how I am distancing myself from 4chan to add validity to my argument?); but I do think more communities could learn something from 4chan in this aspect.
On a related note; I saw that outrage thread linking in the 4chan post about this black chick getting some dude fired and what not about a non-PC joke at a conference. Then, in the HN thread [1], to my pleasure, at least the top comments were mostly absent of the typical reddity/facebook etc. white knighting "This is why women arent in tech!" nonsense.