I believe you're completely wrong about this not being the case on other sites. If you can find even one site that can fairly be compared to HN which is not at least as bad on divisive social issues, I'll be surprised. If I recall correctly, the last time you brought this up you said you were comparing HN to private, controlled forums. That's not a legitimate comparison. I'd bet that those private, controlled forums are far smaller as well. Any such community is going to have a completely different dynamic by virtue of size and structure alone. It's not because the moderators are more enlightened there or less enlightened here. That may well be the case but I guarantee you it's not the high-order bit.
Your argument about this feels to me a bit like backseat driving. All of HN's problems in these areas are endemic to the category it belongs to: a large, public, optionally anonymous, completely open internet forum. Find one of those we can learn to do better from, and I'll be delighted to.
Of course then this becomes an argument about scale, doesn't it? Twitter and Facebook both suffer from problems of racists and issues relating thereof, but do you really, really want HN to be compared to those sites? Do you view HN as having the same issues adapting to scale and being unable to control their userbase? Do you believe Facebook and Twitter to be above criticism because they have little to no other sites they can be compared to?
The sites I'm referring to are more or less microcosms. Larger subreddits, or sites like Tildes, SomethingAwful etc. These sites don't have the traffic of HN, but they deal with similar issues at their own scale. Larger sites can and absolutely should apply ideas learned at smaller scales and try to scale them upwards.
edit: Regardless of my thoughts on the site, I'll stop arguing about it and let things hopefully get back on topic.
Your argument about this feels to me a bit like backseat driving. All of HN's problems in these areas are endemic to the category it belongs to: a large, public, optionally anonymous, completely open internet forum. Find one of those we can learn to do better from, and I'll be delighted to.