I suspect that there are all sorts of reasons for blogging anonymously. For one, the internet is full of crazies (ask PZ Myers, who has received angry phone calls from Powerline fanatics), and I have a child. The last thing I want is one of those insane pro-Evolutionary Psychology freaks to know my name and where I live! But the main reason that I chose to be anonymous has to do with my career. I personally find my career more important than a stupid blog, but I also see no reason to not blog simply because I don't want to step on the toes of individuals who might be responsible for determining whether a particular institution hires or fires me. So, I blog, but do so anonymously. Perhaps someday I'll put my last name at the end of each post, but I can't promise that I will. I certainly don't see any reason why I should have to.
One more thing. In the above-linked post, the always slow-witted Keith Burgess-Jackson writes:
Imagine a world in which there were no anonymous utterances. It would force people to be civil, fair, and charitable; to be responsive to the facts; and to be logically consistent—for the absence of any of these things would constitute a black mark on one’s record.Clearly, he's never actually observed a political debate between onymous pundits. Hell, he's apparently unaware of the bulk of the political discourse in this country, period. Only a fool would fail to notice that the absense of anonymity does not force people to be civil, fair, and charitable, responsive to the facts, or logically consistent. But since KBJ blogs onymously, and exhibits none of these features, it's not surprising that he's failed to notice this.
UPDATE: The Anal"Philosopher" has more to say on the topic, here. Once again, he demonstrates the civility, fairness, and charity that makes him so representitive of the onymous bloggers of whom he speaks.