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.
Eh, up votes are just as likely to be an “I agree/like” rather than a topicality, importance, or quality indicator. And it’s just as likely to be done without any engagement worth seeing.
This is also a way to form bubbles/echo chambers since sorting by anything but new will surface just the stuff most agreed with.
If down votes are broken, then all votes are broken. The only way for voting to be not broken is to have them not change what all users see. You’d have to use some other metric for sorting that isn’t time based, and specifically exclude any vote based sorting at all.
Which is entirely possible, and I think that’s the way it should be. Keep votes because they work to filter out useless comments to some degree, but don’t let them matter.