My anecdotal experience, HN upvotes informative, constructive, and positive comments. And it downvotes negative/cynical, political, or unsubstantive comments. I have had comments with very similar arguments, but different delivery receive very different treatment.

Also, if you are trying to recover karma, stick to the less controversial topics. It is near impossible to get downvoted when providing informative comments on more tech/programming oriented topics. Alternatively, create a throwaway account for the controversial threads. Added bonus is that switching accounts will give you a nice pause to rethink whether commenting on said thread is really worth it in the first place.