I think I’ve settled on the latter. Disagreement is maybe best communicated by the absence of an upvote? And downvotes work best when they signal something that is just off base, and while not reportable, is not appreciated at a broad cultural level.
Depends on what kind of “I don’t agree”. If somebody asks for people’s favorite food, I’m not going to dislike all other answers… But if it’s a more serious question, and an answer just has a really bad take that I don’t agree with, that’s getting a dislike.