I don't think I agree with this. Remember that downvotes on SO only have a cost when they're cast on answers, not questions, and that cost is a fraction of the gain from an upvote (1/2 for suggested edits to 1/10 answers).
It makes sense for downvotes to be free on questions and expensive on answers because questions are low effort while answers are high effort, and the community wants to encourage more answers.
On HN, everything is low effort, and everything is worth 1 point. Also, our problem with comments isn't that we don't have enough, it's that we have too many low effort/factually incorrect/abusive/spammy comments that we need to discourage. So it makes sense to keep downvotes free.
It makes sense for downvotes to be free on questions and expensive on answers because questions are low effort while answers are high effort, and the community wants to encourage more answers.
On HN, everything is low effort, and everything is worth 1 point. Also, our problem with comments isn't that we don't have enough, it's that we have too many low effort/factually incorrect/abusive/spammy comments that we need to discourage. So it makes sense to keep downvotes free.