I'm glad you have a sense of the culture HN is trying to cultivate. Even getting just that across is astonishingly hard. By far the likeliest default is that nobody has any sense of it.
Does it fall short? Sure. The question is how much is possible on the internet—specifically on a large, public, optionally-anonymous internet forum, the bucket HN falls in. We're happy to do our utmost, but only along the axis of the possible. We can't come close to delivering everything people imagine and demand. Your comment doesn't allow for the constraints we're up against, how few degrees of freedom we have, or how close we come to getting crushed between the gears.
HN is a large enough population sample (5M readers a month) that it is divided wherever society is divided. That means you're inevitably going to see posts which represent the worst of society relative to your own views. Societies, actually, because whether you doubt it or not, HN is a highly international site. People post here relative to their respective local norms, but mostly in mutual ignorance of that fact. This accentuates how bad the worst posts seem.
So yes you see awful posts, but it doesn't follow that they're representative either of the community or the culture. Jumping to that conclusion is an error nearly everyone makes, because painful impressions (such as nasty comments) are vastly more memorable than pleasurable ones (such as sensible comments). This has been studied and there's a name for it: https://en.wikipedia.org/wiki/Hostile_media_effect. The phenomenon was established about news coverage (https://www.oxfordhandbooks.com/view/10.1093/oxfordhb/978019...), but internet comments are no different.
What are these "other sites and circles" you mention that do so much better culturally than HN does? Are they public forums where anybody can create an account? Are they optionally anonymous? How large are they? In other words, do they face the same problems that we do? If so, and they're better than we are at solving them, please point us there so we can learn from them. Nothing would make me happier. Usually, though, when people make this claim, they're talking about much smaller communities and/or ones that are not fully open.