By default, Lemmy allows downvotes globally. However, when a server disables downvoting, it is similar to using a feature that is usually reserved for enterprises and very small, non-federated communities.
If a user prefer to not see downvotes, they can disable it by his favourite client settings, but the rest of the community should not miss this functionality for the pleasure of few users.
It always will be. I think their should be a ranking where the closer to 50/50 the votes are multiplied by the magnitude of votes is thw score. If people like as much as dislike it surly is adding the most to the conversion.