Here's something for you: HN has groupthink (er, I mean PG-branded Orthodox Privilege) in spades. If you agree with the Group (orthodoxy) you get upvotes and lots of kudos. If you don't, you get downvotes and criticism.
The incentives encourage people to downvote rather than criticise. If they post a critical response, they run the risk of being downvoted by those who disagree with that criticism. You can't get downvoted for a silent downvote.