But yes, race-related discussions are fraught, and there's little doubt that race-related, if not racist, beliefs and feelings lie behind some of what people say in them.
Given the context (American society and history), the situation is unlike other controversial topics. It's like comparing critical decision-making to kneejerk reactionism; we just can't seem to help ourselves. I feel like that's worth pointing out, above and beyond simple exhaustion with the "Actually" crowd.
After that first wave of comments, we frequently see a second wave of comments reacting in a reflexive way to the first wave. Although they take the opposing position—defending the article and criticizing the comments—it's the same contrarian dynamic, the same mechanism, driving them. Usually the second wave gets upvoted the most, leading to the paradox of the top comment in a thread expressing how bad the thread is, or the most popular comment expressing how wrong the populace is.
There's a place for such comments, and it wouldn't work to exclude them anyhow. But their rapidity means that they add less information. That's not because they're shorter (though it does take longer to add more information). The problem is how predictable they are. They're fast because they're largely precomputed—they're really responses to past things, stored up and ready to fire when a similar-enough signal arises. Comments like that make for repeats of past discussions, which are less interesting. They don't gratify intellectual curiosity. https://news.ycombinator.com/newsguidelines.html
Comments that add new information, rather than repeating what has been thought or felt or said before, tend to be reflective rather than reflexive. This happens when a topic sparks a new thought or feeling, or touches an unusual experience one has had. These comments add new information and encourage discussions that aren't just repetitions of old ones. But they require processing time: they have to be computed from scratch, not just fetched from cache. It isn't just that they take longer to write, but that it takes longer to form new pathways. It also consumes more energy, which means that reflective comments tend to come out quieter and more delicate than reflexive ones do. And they take more time and energy to read, too, so replies are more likely to be reflective in their own right.
The task of HN can be summed up as: how can we nurture reflective responses and give them priority over reflexive ones, given that the latter are both faster and stronger? How can we get into a reflective-reflective cycle rather than a reflexive-reflexive one?
I agree with you about race relations being a force multiplier on this (and also ). But I'm insisting on the more generic issue of contrarian dynamics because it shows why you can't conclude that negative comments, which spring up like mushrooms when a thread is fresh, represent the community. It's a non sequitur, for example, to imply/conclude as you did in https://news.ycombinator.com/item?id=21474980 that HN's community must be racist because the comments found fault with the article. That phenomenon is generic: the comments always find fault with the article . The fact that the community upvoted your comment to the top (where it was sitting before I moderated it) suggests that much of it is aligned with your view. This interplay between votes and comments is typical.
Most of what we see on HN is so determined by the basic structure of the internet and the initial conditions of this forum that I appreciate McLuhan's "the medium is the message" more every day. It is far more deeply true than I ever realized.
 You're right that the context of American society and history makes the topic of race especially charged. But it's even worse than that here. HN's audience is at least half outside the U.S., leading to additional externalities and conflicts that look like something other than what they are, and so are particularly difficult to understand. This overlaps with the American context in inflammatory ways that make the threads both worse and harder to recover from. Basically everybody is fighting from their own, often very different, context and history without even realizing that they're doing it.
 That phenomenon is also far stronger than it appears to be, because as moderators we're constantly doing things to counteract it. If we didn't mark shallow dismissals and reflexive negations as off topic, which lowers their rank on the page, they would probably dominate every thread.
The answer to the issue is fairly simple but relies entirely on the humility of HN's userbase, particularly in regard to topics that seem easy to expound upon "logically" but for which they generally are lacking in knowledge of or experience with.
Therefore, I have little hope.
I'll keep pointing out the fallacy when I see it, though.