My somewhat satirrical definition of Hard Science Fiction is “Anything that reads like a cross between an engineering textbook and a right-libertarian tract”. This might be one cause of the sexism in the SF world, in that few women are interested in writing that kind of stuff; they insist on having things like three-dimensional characters.
That was something that turned me off consistently with most of the "new hard SF" I kept coming across: it was a race between the techno-porn or the politico-porn to see which would constitute the bigger audience endurance test.
Now that I think about it, though, those two things seem to come joined at the head for a reason. The latter is the theory and the former is the practice.
I always imagine the thinking about such things goes something like this: The universe will be ours, and anyone who gets in our way of claiming it as our right and our destiny is just a big poopyhead, and here's all the nuts and bolts of how we're going to go do it.
It's not the actual goals I find obnoxious, or even undesirable. I'd love to know that, as a species, we're not going to die unmourned on this lump of rock by drowning ourselves in our own waste products. But I can do without the political window-dressing and the sneaky excuses just fine, thanks. Your average episode of Gundam ends up being more astute about such things, and carries far less ideological baggage in its trunk to boot.
Back when I started writing Flight of the VajraI made a joke that one of the reasons I was doing it was to write a space opera that didn't have a single space marine in it. Later, I realized I was actually half-right: I'd been trying to write an SF novel where things like the military or normative far-future technologies or what have you are elements in a whole, rather than justifications for the existence of the whole. I wanted to show that even the people who ostensibly seem like the Bad Guys are not wholly wrong for being disgruntled with the state of things; it's their methodologies I object to more than their dissatisfaction per se.
And, finally, I wanted to have that story built on the backs of an identifiable cast of fully-realized characters. I suspect Tim's comment about sexism is partly right, since many such works of SF seem incapable of thinking of women as people. But I'm wondering how much of that sexism is simply a symptom of a far deeper, more pervasive problem — that of most SF being unable to think of people as people.