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.
That’s what a lot of us agreed it was for a long time ago, but most people use it as an “I don’t like this”, or “I disagree” button. Some people even use it as an “I don’t like you personally” button. There were a few times on Reddit when I got into an argument with someone and they went through my profile and downvoted everything they saw until they got bored.