A bit of me wishes that the "no mindkiller topics" rule was enforced more strictly, and that we didn't discuss sex/gender issues ... We already rarely discuss politics, so would it be terrible to also discuss sex/gender issues as little as possible?

I agree - I think the weakening of the taboos against discussing politics and gender has been a seriously bad thing. The arguments used to establish these taboos are in retrospect unsatisfying (for example, the explicit argument used for the politics taboo did not support nearly as strong a taboo as we in practice actually had), so people can easily come up with plausible accounts of how we can avoid the ill the taboo prevented without needing the full force of the taboo. However, I think these accounts are poorly motivated; there are deeper reasons against discussing the mindkillers. Whilst a particular style of conversation might avoid the particular danger that attention was brought to, the underlying issue is still there, so other damage will be wrought instead.

I don't see much way to enforce this though, as it's a tragedy of the commons. My best guess is to persuade enough people to just reflexively downvote anything to do with object-level politics or gender (including posts masquerading as meta-level).

If I try to tell by the way people are acting, I'm half convinced that most of the people here think I'm a moron.

Perhaps comments suggest this (though I admit I generally find LW a very freindly place, so maybe we just read comments in a different mental tone of voice), but I think it's clear this is not true of karma. If your comments are being upvoted then, at least by the origional states interpretation of karma, people "want more of" your comments.

In general, in fact, most comments are upvoted; only the very worst are downvoted. Indeed, it tends to be the freindly, jokey comments, rather than serious ones, that get upvoted the most. This encourages people to post more and more, as they get the positive reinforcement, but the money-illusion (karma-illusion?) means they don't realise the currency is being debased.