If you want to just stop at one, or the minimum, well, I guess that's fine. But some prefer to express themselves with more than the minimum. Do you want to just do the minimum?
Teenagers will frequent this site, and will say stupidly naive things about topics they know nothing of, and they will grow from it. It happened to me, it happened to you.
It's not about people consistently bringing their A-game to HN because it's higher tier - most of its users are not far from their teenage counterparts.
A very small minority of experts will weigh in on one topic, and because their audience is a few hundred people instead of a few tens of thousands, a discussion can actually form.
Experts exist on every public forum in the world. Whether they are heard or not makes the difference. It's quantity that's the detrimental factor.
I think I know what you mean, but even if I disagree with the professionals, I can't help but respect that their opinion is likely more informed than my own, at least in the high circles they revolve in.