On HN I almost never downvote. On reddit this was different. Not sure why but I feel that on HN karma is so much harder to get that I don't want to be an obstacle. On reddit I could more easily downvote. It also was easier to get karma. (Reddit is annoying with regards to its censorship though. That is one arbitrary censorship over there ...)

I downvote obvious fallacies and bad faith. And people who fan the flames in a thread. I don’t downvote posts because I disagree with them, but that’s just me. (I don’t upvote because I agree either)

Overall, it is common to see greyed posts downvoted for questionable reasons, but I don’t think I’ve ever seen a dead post that did not deserve it. So overall it seems to work and I avoid overthinking it.

But that means more people will get enough karma to be able to downvote, and they likely won't share the same ideals as you so they will downvote more often, making it even harder than it already is for new users.