The users are deciding. We are flagging these stories because we don't see the value in endless flamewars over the same subject. If you can't get enough of debates about sexism in SV there are lots of other places on the internet for that.
After all, for some of these topics it's exactly the people that won't go looking for them at other places on the internet where they may still make a difference.
To use an example that's slightly less controversial: I think it's important for people working with lots of other people's data to have some fundamental sense of privacy rights. And HN is probably one of the best places to reach those actually in the trenches that are in the position to say 'no' when, for example, the CEO of Yahoo tells them to allow the NSA full access to their users' emails.
Yet that's a topic that quickly turns to politics, so you'd probably have good reasons to wish those discussions happened elsewhere.
Just to be clear: I think the mix of topics overall is mostly fine right now. But just like Facebook or Twitter, I think HN may be in a position where your "editorial responsibility" should be somewhere on your radar. Not because HN is the size of those, but because it caters to a readership that has certain powers far outstripping its size.
edit: not sure why this is getting downvotes when it's a direct counterargument/response to the parent