I wish more people would see that it's OK to think the original joke isn't particularly offensive (I think it's fine) while simultaneously acknowledging that it might make some people uncomfortable and that we should try to show some empathy for those people instead of making comics and t-shirts to mock them.
Many people feel disenfranchised and ostracized because of this incident and I think we could all benefit from trying to see the story from that perspective instead of thinking things like "this doesn't offend me, so what's the big deal?"
The "fear" of doing that is that people don't want to give any excuse to then censor those types of jokes. Like, why even voice your displeasure and get blog / article hits? It's either for advertisement or an end goal (usually).
Add to that the idea that maybe they shouldn't have been offended, period, and you have a hilarious explosion of outrage and book-length blog posts.
I'm not saying it's right or wrong, by the way. To me it'd be easy to say "Hey, sorry you were offended" and leave it like that. Mike aggravating the situation actually makes it harder to say "I like Penny Arcade", and that honestly and truly sucks.
He really strikes me as that guy who goes "This far, NO FARTHER!". That, combined with earlier being bullied and the perceived "What's the protesters real endgoal?" probably provoked the response he gave. He wants to not backdown and make sure everyone knows he didn't back down.
Which makes our lives suck.