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.
Downvotes should be for off topic posts/comments or spam.
Disagreement is best communicated by replying saying you disagree and why. It’s a discussion forum. Talk.