On LessWrong, we often get cross, and then rude, with each other. Sometimes, someone then observes this rudeness is counterproductive.
As a general rule, emotional responses are winning strategies (at least for your genes). That's why you have those emotions.
Granted, insulting someone during your rebuttal of their argument makes it less likely that they will see your point. But it appears to be an effective tactic when carrying on an argument in public.
It's my impression that on LessWrong, a comment or a post written with a certain amount of disdain is more-likely to get voted up than a completely objective comment. A good way to obtain upvotes, if that is your goal, is to make other readers wish to identify with you and disassociate themselves from whomever you're arguing against. A great many up-voted comments, including some of my own, suggest, subtly or not subtly, with or without evidence, that the person being responded to is ignorant or stupid.
The correct amount of derision appears be slight, and to depend on status. Someone with more status should be more rude. Retaliations against rudeness may really be retaliations for an attempt to claim high status.
What's the optimal response if someone says something especially rude to you? Is a polite or a rude response to a rude comment more likely to be upvoted/downvoted? Not ideally, but in reality. I think, in general, when dealing with humans, responding to skillful rudeness, and especially humorous rudeness, with politeness, is a losing strategy.
My expectation is that rudeness is a better strategy for poor and unpopular arguments than for good or popular ones, because rudeness adds noise. The lower a comment's expected karma, the ruder it should be.