Are... are you serious? Or is it just trolling? I'm not an obsessive HN reader but I see sexism stories show up at the top of the HN list all the time. To the point that I've taken it as one of the odd HN cultural quirks, that you all like to discuss it obsessively. Claiming they get "buried" is contrary to all evidence I've seen, though I guess if you have statistics I'm willing to be proven wrong.
What are you talking about? I see at least a few stories per week on sexism in the top 10. Given that this place is more technology/startup-related than "let's talk about society", that's a pretty good frequency for just one of many valid social causes.
Next time you see a story about sexism against women (redundant but needs the clarification here anyway), watch its movement. Yeah, it may get up in the top for a bit, but you can watch stories that are older with fewer points and comments move up above it. Happens every time.
I've seen this effect in other "heated" discussions, and I wonder if it's the effect of moderation. Primarily, what happens to a thread as the percentage of moderated messages increases? Is that metric involved in the positioning? I could see a topic like sexism (or emacs v. vi) getting an inordinate amount of moderation, and thus might be flagged more often, moving it down the list. Maybe that has nothing to do with it, but I've seen this effect before.