I will go so far as to say your suggestion to "focus on the problem in full generality" -- which is to say, to completely encompass an impossibly complicated issue -- is just a way of trying to pass responsibility and to avoid admitting that there is a problem. Of course, trying to resolve sexism everywhere is admirable. But to use the existence of sexism in other fields as a reason to avoid addressing it in our own is little better than rejecting its existence altogether.
edit for your edit: I think there are specific reasons that sexism is more prevalent in tech, which are not necessarily related to "software people are ignorant". In our culture there appears to be a general bias against women in pretty much all STEM fields, perhaps for historical reasons. I suspect (although this is just my opinion) that this is largely responsible for any greater bias that exists in tech as well. There is a mistaken perception that women are less capable in highly rational pursuits, which affects how women in tech are viewed by their colleagues. I think this is a big reason that women have a hard time in tech.