Like Feministe, I've always found it a little odd to read nominal progressives in the blogosphere offering attacks like… well, I'll just quote:
Jeff Goldstein is a paste-eating 'tard. Ann Coulter is an anorexic cunt with an Adam's apple. Hey Michelle Malkin, me love you long time!
Something else I've noticed, that may explain what's up with that: Some of my liberal friends—people I'm as sure as one can be have not a homophobic bone in their bodies—will use "fag" as a casual pejorative (though never directed at an actual gay person except by another gay person); the conservatives and libertarians I know never will. This seems (and seemed to me) strange on face, but I think it makes sense for two reasons.
First, at least among people who know him, the progressive can probably be relatively confident that the hateful views we associate with that term aren't going to be imputed to him. The conservative (I'm talking about the sort of conservative I'm capable of being friends with here, which excludes the actual bigots) will probably be acutely aware that there are plenty of conservatives who harbor those views, and especially keen not to be mistaken for one of them. Think of how you'll find people who know each other well making tongue-in-cheek jokes based on each other's race or religion or orientation or whatever that they wouldn't dream of uttering in a public setting. (In a weird way, the ability to exchange such "offensive" jokes is a sign of friendship: If someone you'd known for a long time never prodded you or had fun at your expense or generally gave you shit, you might take it as a kind of formality suggesting a lack of closeness. (Update: Commenter JK points to a Slavoj Zizek interview with some interesting thoughts in this vein.)
Second, one reason that jokes like that are actually funny—one reason the South Park kids' "Jew" and "fat fuck" banter works, or at least worked when the show debuted—was that because they're rooted in genuinely offensive attitudes, they still retain the power to shock that's necessary for that kind of humor. "Fucker" and "shithead," while more likely to raise hackles at the FCC, wouldn't have the same frission, because what you're actually going to laugh at has to at least flirt with the violation of your own taboos. My recollection (I'm too lazy to check this now) is that the evolutionary function of laughter is to serve as a kind of "all clear" signal in the face of apparent danger. Somone tickles you—but it's not a real attack, though it might look like one—and we laugh. Most verbal jokes turn on either some kind of reversal of expectations or the harmless violation of taboo; slapstick is all about the appearance of injury without actual harm. Someone stubbing her toe isn't funny; someone falling and cracking her skull isn't funny; someone doing a wild pratfall, then sitting up shaking her head, dazed but unharmed, might be hilarious. The more dramatic the pratfall, the funnier it is when it proves to be harmless; the stronger the taboo, the more potential humor in its ("harmless") violation.
So it seems like you might find racist/religious/sexist/etc epithets or jokes in two very different kinds of context: First, sincerely, among actual racists, sexists, and other bigots. Second, in groups where there's a strong taboo against those actual attitudes, but the people communicating are sufficiently confident of themselves and each other on that score that boundary-pushing results in that all-clear humor reaction. The problem on the Internet, of course, is that you often end up with a forum that feels like a small close knit community but is actually available to thousands of casual readers—a tension I expect we'll be negotiating for a long while yet. Anyway, that might be one reason you find the kind of rhetoric the Feministe folk were so appalled by in particular among the blogs and chat boards of the left, where people are both especially likely to be conscious of speech taboos and confident that everyone's actually got the right sorts of views. [Cross-posted @ NftL]