It doesn't.
Admittedly, HN discussion is generally of higher "quality" than Reddit, at least for large subreddits, but that's a very low bar to hurdle.
> The HN welcome page lays out two cardinal rules: don’t post or upvote crap links, and don’t be rude or dumb in comment threads.
These cardinal rules are routinely violated.
A rational person would just read the linked articles and ignore the comment section. HN is still the best link aggregator, I think. Unfortunately, I'm irrational and prone to pointless argumentation, which is why I sometimes show up in the comments. (Duty calls.) I usually regret it, though.