I seldom upvote (and I can't downvote). Why bother? Can't see whether or not it's had any appreciable effect. Can't see the vote count. I already know other signals are used to determine rankings.
HN makes it hard to read a downvoted comment by dimming it. That has acted as a demotivator for me to downvote a heavily downvoted comment. I upvote them in the hope that I will be able to read them.
Not that this is the same thing, but in case you didn't know you're always able to read comments on HN, even redacted ones, by inspecting the stylesheet. I really like this compromise that they've made.
CTRL+A solves this readability issue easily, but I don't think this (dimming) is the right way treating the comments (HN should just allow sorting like Chronological, most upvoted, basically Reddit sorting since it use reddit tags anyway) and just display everything according user setting. I also don't like flagged comments being collapsed, no matter the reason they are flagged for, anyone/any brigade/bots can hide this way comments they don't like.