When I "know" a comment is factually wrong, especially when the tone is of great confidence and putting down or rebuking people who aren't. When a comment is h

When I "know" a comment is factually wrong, especially when the tone is of great confidence and putting down or rebuking people who aren't. When a comment is hostile in a way that discourages discussion, or there is a long argument chain consisting of low-content/ad hominem/childish back-and-forth. When jokes are not funny. I upvote when they make me laugh, but HN is known to be humorless because of the downvoting of anyone making "unserious" comments. When someone is repeating or spreading what seems to me to be propaganda or political talking points, especially when those haven't already been brought up previously and don't have special relevance to the discussion. Downvoting can serve as a weak signal of popular consensus (weak because the comment ranking algorithm seems to take author's total karma, time since posting, and relative age of the comment into account as well). They help me as an author of comments to recognize when I have been too harsh, impolite, uncharitable, poorly worded, etc, but it's not always clear why some comments get downvoted. Sometimes there seems to be brigading or botting, but I obviously don't have the ability to know or definitively say whether it actually happens or not. As a user I don't feel downvoting benefits me much other than providing an invisible outlet for expressing dissatisfaction, especially when I wouldn't be able publicly express it in a polite manner. I find it very annoying to see greyed-out comments and having to highlight them to read, and I hate the sorting of comments by score rather than date.