To be scrupulously fair, I probably ought to find the equivalent making fun of how liberal pundits argue; they can get pretty shrill, too. I have no use for anybody, right or left, who can't laugh at themselves a little.
Really, very few people know how to argue well -- although bloggers do much better than email posters, on the whole. The amusing thing is, some of them aren't even aware of it. I don't know how many times somebody will claim to have "proven" something, when they haven't proven it at all. The flip side is to dismiss evidence that you don't like as irrelevant. Denial is an easy technique to pull out of the hat; you can drive your opponent to distraction by resp0nding to everything with "No, that's not true" a dozen times. Then, when you get tired of that, you can go ad hominem.
It's a rare poster that doesn't go the ad hominem route, at least some of the time. Even I have been known to do so in moments of exasperation -- although it is usually of the "go jump in the lake" variety, rather than name-calling. (Yes, I know I called Pipes a crackpot, but I think that's a comparatively mild epithet, considering what he was saying.) Sometimes the technique appears to be to overwhelm with simple nastiness so that the opponent abandons the field and you can declare victory. While there's plenty of nastiness in blogs, at least you don't run into that kind of directed viciousness. I don't think anybody closes up their blog because opponents get mean, but forum posters will frequently decide that an argument turned into a slinging match is not worth their time. Also, the slugfests are shorter-lived on blogs. There may be blogs out there that consist of nothing but attacks; I'm still new to this. But I've seen flame wars on forums last for months or years to the point where there is no substantive argument at all, except about who is the biggest asshole, which is of scant interest to observers.
My favorite comment on ad hominems comes from Michael McKenny, who has long maintained that one should respond to them by thanking the attacker for conceding the superior strength of one's argument. If, after all, they are resorting to personal insult, they probably haven't got anything better to counter you with. But in the heat of the moment, I seldom remember to take that good advice.