Shaker Abra just sent me the link to a post at the New York Times' Freakonomics blog, in which Justin Wolfers proposes his theories as to why the vast majority of his hate mail comes from men. (Or, why women don't write hate mail. Duh. Because they're from Venus, and on Venus we use telepathy.)
The comments explaining why men write hate mail are particularly hilarious. Personally I really liked "Evolutionary drive to utilize the 1 billion extra brain cells we have when compared to women" and "Since we no longer are required to leave our campsite, hunt down, kill and drag dead carcusses [sic] back home, arguing via long distances must be the next best thing."
Suffice it to say, I don't think there's a pat answer to this question, but, being an uppity woman with an internet presence, I get my fair share of hate mail (99.9% of it from men, who are quite keen to let me know they are men), and the tenor of their collective emails is wanting me to shut up, close up shop, go away, die. It's not enough that they don't have to read what I write; my mere existence is so abhorrent to them that they can't bear to not write.
The common thread is the attempt to intimidate me into shuttering Shakesville. It's not just aggression, but a particular kind of aggression—a bullying, threatening, eliminationist kind of aggression.
And, given that the vast majority of my male correspondents, even those who disagree with me, don't display that kind of aggression, I don't feel remotely inclined to suggest that particular kind of aggression is intrinsic to men. It may, however, be significantly more common among men because they are infinitely more likely to be socialized to use brute force and harassment to get what they want than are women.
I don't know what Wolfers' hate-mailers want from him, but I suspect it isn't all that different from what my hate-mailers want from me—a reaction, a show of fear, some sort of communication that we have been suitably intimidated, and, in the best case scenario, our slinking off into the ether for fear that our hate-mailers will make their dark fantasies our reality.
There's another possible component to this, related to the internet generally. Women's participation in general-audience internet communities tends to be very different from women's participation in women-centered spaces, largely attributable to commenting policies and community rules that, even when there are guidelines re: hate speech, tend to turn a blind eye toward misogynistic slurs and female-specific harassment and silencing techniques.
The ubiquity of forums that disregard how alienating such casual acceptance of misogyny is, has certainly discouraged many women from participating in internet communities the same way men do, operating as silent observers rather than vocal contributors. (And even women who participate using androgynous or an overtly male name, to avoid harassment, often can't honestly and fully participate without compromising the key part of their identities they have secreted away.)
It would be foolish, in my opinion, to discount what affect that has on which sex is more likely to give feedback. We are both, after all, whether from Venus or Mars, creatures of habit.