Even if there was a more prominently stated, formal policy about when downvotes are appropriate, it would make no material difference; the overwhelming majority

Even if there was a more prominently stated, formal policy about when downvotes are appropriate, it would make no material difference; the overwhelming majority of downvote-inclined people will downvote any comment that gives them a negative feeling. That said, some of the best comments are ones that carry an argument that most people would disagree with, but are worded persuasively and/or informatively enough that they attract upvotes. It's difficult to achieve but well worth aiming for. Outside of encouraging that, I'm not sure what else dang is meant to do. Discussion platforms that try to enforce policies like requiring explanations for any downvotes don't seem to have substantially better quality discussions.