The problem is with your second paragraph is that these days, being annoyed can be used as a weapon. So we're back at "humans are involved". But I think, even

The problem is with your second paragraph is that these days, being annoyed can be used as a weapon. So we're back at "humans are involved". But I think, even more fundamental than people being annoying and being annoyed, some people are acting in bad faith. Some people are there, essentially, as agents - of a nation, or a political party, or a viewpoint. They are there to declaim, not to have a conversation. This is incredibly destructive to communities. For a small community, I could see a moderator having the ability to ban users from the site, but also the ability to ban users from a thread. "On this topic, you're not acting in good faith, so you're done for this thread." It wouldn't scale to HN, of course - dang is busy enough as it is. (Of course, this presumes the moderator is acting in good faith. But if they aren't, the site turns into an echo chamber for the position the moderator supports, and the reasonable people go somewhere else.)