If you want good comments then you have to prevent the down-voting of factual statements simply because the people who vote disagree with those facts, as happens repeatedly on HN.

-1, Disagree is poison for quality commenting.

I used to be serious about SMO on Reddit and believed that downvoting behavior drove what got the top more than upvoting for links which had a lot of consequences, like if you posted to /progitt anything that let on that you were into coding for the money, even partially, or thought the business side was interesting… oh boy. HN is not like that.