This comment seems guilty of most of what it's complaining about.

The HN community is pretty evenly divided. People who strongly favor one ideology routinely imagine that HN favors the opposite one. They can't be right, though, because their various complaints are contradictory.

I think it's because the ideological mind feels surrounded by enemies. When it sees something that it agrees with getting downvoted, or something it disagrees with getting upvoted, it feels aggrieved and jumps to a conclusion of general bias.

It's true that comment quality has declined, but not because there's a dominant ideology. It's because larger groups are stupider.