When comments get downvoted rapidly here, it is usually because their
tone is deemed unacceptable by the community. Which, yes, is unabashed tone policing in the most literal sense of the word - but I think that's exactly why HN is much more pleasant to have conversations on than most other platforms online these days.
Also, when something gets downvoted solely for content, if you come back later, it often gets upvoted right back (and then some), with some comments below to the effect that downmodding is not a proper way to express disagreement. I've upvoted greyed-out comments that I strongly disagreed with myself more than once, solely on the basis that they make a valid argument that ought to be a part of the conversation - even if only to debunk it properly.