If the participants are doing a good job of explaining where they're coming from, then yes. If they're just talking past each other, or worse, angrily insulting each other, then of course the answer is no. At that point it's no longer really a discussion at all, it's the online equivalent of monkeys throwing filth at each other, and it debases all involved.
> > where both sides end up arguing the same philosophical issues over and over again
> Funny, I would describe HN as the same.
Sure, some hot topics will keep coming up until the end of time. Copyleft vs permissive licences, for instance. I think that's fine though, and the ongoing discussion isn't pure retreading, it will evolve over time as the surrounding circumstances change.
A discussion forum like HackerNews shouldn't aim to be the equivalent of StackOverflow where there's a single authoritative page for each question, and duplicates are rebuked and shut down. That approach makes sense if you're trying to build a question/answer repository, but a discussion forum is something different.
> I don't share the common HN conceit that commenters on HN are better than elsewhere. IMO there's no evidence of that
My opinion is no more well grounded than yours, but I disagree. HN discussions very often have input from experts. Anecdotally I think this happens less often on other forums. HN also has uniquely good moderation.