Not every platform on the fediverse has a downvote system, but those that do (Lemmy, piefed) are heading down a bad path, imo. Downvoting is one of the worst features of reddit, leading to dogpiling, group think, and silencing of minority viewpoints. I do see the value of it, on the surface, and if you want to enable it for yourself to allow certain posts to be downvoted for your own information, I think you should be allowed to do so, but having it set as default for all posts just leads to a toxic and conformist environment, which is what I thought the fediverse was trying to get away from.
I believe Piefed let’s you restrict downvotes to people that are subscribers. I think that’s a good solution to idiots downvoting from all just because they’re not interested in or understanding the post and/or the community it’s in. I also wonder if people even understand that they’re not training an algorithm, just dragging people’s posts down.