Strict moderation is the reason HN is the only reasonable discussion forum remaining on the internet. I wish good moderation was a skill that more people learned - would you ever be interested in writing a guide or teaching a class on moderation?
Not at all. It's rather the community that makes it a reasonable discussion space. Most people here understand that this is not Reddit and that proper answers are needed when you interact with other members. Of course moderation is useful and necessary in certain cases, but it's certainly far from being the key factor here.
Enough HN members are happy to feed the trolls (even if unwittingly) and encourage more without removing them.
Downvoting, flagging works even when the mods are not around. I am pretty sure that a comment flagged too many times is greyed out and almost invisible (and that happens without mods).
Again, if we are to believe there are only 2 full time moderators on HN for the amount of comments going every single minute, it's virtually impossible to rely on mods alone for proper discussions: simple maths.