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.
It's easy when a community is small. The more prominent the community gets, the more it tempts people who enjoy stirring things up.
In the end I'm not sure if any moderation scheme can prevent that, to be honest. There will always be people who consider it a challenge to see what they can get away with, either by trying to stay just under the moderators' radar or by returning every time they're banned. Provocation makes people defensive, and then their own replies turn harsh, contributing to a negative perception of the community.
I do hope that this community avoids it as long as possible. I've discovered it only recently and am enjoying it. But past experience suggests that it, too, will one day degrade.