> Part of me wishes HN had a really strong moderator that slapped down nay-sayers. If you're not contributing something valuable, comment deleted.

What a load of rubbish. Note that HN already has strong moderation, and does delete "way out there" contrarian views. If this was taken to the extreme, only back-patting allowed, the comments would become useless. And I feel, like others, this already goes on a lot (e.g. the top karma posters all tend to agree/compliment each other, there isn't that much disagreement although it happens sometimes).