I have to credit 'dang and 'sctb's public moderation and tone-setting for a lot of it (and I've been a critic of weak and permissive moderation here in the past, so credit where credit is due). HN still has some really profound problems with punching down, but so does everywhere else and it's improved significantly; amongst the places I hang out it's gone from perhaps the most egregious example of the kind of nastiness in the industry to somewhere better than the median.