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.
What is needed is better controls over who can downvote. Communities should get better controls for moderation - up to and including control over whose votes get counted. Simple controls like “only subscribers” or “accounts older than 1 week” or “accounts that have commented on the post/replied to this comment” all the way through to “only users on this list”.
But pushing the control into the individual user’s hands will simply create echo chambers worse than the existing ones. Let’s not turn Lemmy into Facebook.