Having experienced platforms with just upvotes, and platforms with up/downvotes, I really think downvotes are bad - for me at least.
I think it encourages laziness - much easier to just downvote someone than actually critique them. It also makes me hesitate to post something mildly controversial or against the grain through fear of being penalised. I’m speaking for myself here - I’m guilty of both of those things.
That’s one of the reasons I’m on Beehaw, because Beehaw doesn’t federate downvotes I can neither see them nor give them - and it just feels like a much nicer Lemmy experience - and I feel like it makes me automatically nicer to people as well.
(n.b. You can hide downvotes in settings on any instance, but you can still see them by hovering over the score and it still affects comment ranking - unless you’re on Beehaw or something else that does similar)