The two extremes are: 1) everyone upvotes to agree (and only to agree), and downvotes to disagree (and only to disagree). Then the score on a contribution meas

The two extremes are: 1) everyone upvotes to agree (and only to agree), and downvotes to disagree (and only to disagree). Then the score on a contribution measures its proximity to the average opinion. 2) everyone upvotes signal and downvotes noise. Then the score on a contribution measures its relevance to HN readers. Since I don't care about average opinions but much about relevance, I upvote and downvote by rule 2).