That former group has disappeared, and 4chan has become the biggest echo chamber on the Internet. There are stretches of hours and thousands of posts where there isn't a single dissenting political opinion.
The irreverence of 4chan was always the appeal. It has morphed into a lockstep belief system in a hero figure. What's the point of a website with anonymous posts and no rules if everyone is carefully agreeing with each other?
Basically, the idea of being racist is so absurd, that by being ironically racist I'm poking fun at the racists, not the races.
It's not a completely ridiculous notion (though it's abused heavily); satire is a common tactic for comedy. Clearly people go too far, and I don't think it's a good excuse to say "it's just satire".
I'm not exactly sure where we draw the line socially. I don't really have a problem with something like The Colbert Report, but I also really hate the "shitlord" movement that seems to be happening.