Coming from Beehaw, which always had downvotes disabled, I don't think downvotes are necessary for a healthy Lemmy instance. More popular content will naturally surface by virtue of having more upvotes; there's no need to have a mechanism to "pull down" less popular content.

I also think that downvotes are too easily abused or weaponized. It's trivial to downvote bomb all of a user's or a community's posts. Without downvotes, to achieve the same effect, you'd have to upvote every single other post that exists.