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.
People who mass downvote, with or without scripts, are better dealt separately - it’s vote manipulation, those people shouldn’t be voting up or down on first place.
You’re still doing two clicks to downvote someone, instead of just one. And in the meantime there’s always some room to think “why am I downvoting this again?”
And perhaps I’m judging other users too much based on my own usage of the downvote button, but often I’d rather have a way to say why I’m downvoting it - because someone were rude, or because they’re babbling bullshit, etc. I tend to believe that other people are like this too, but perhaps I’m wrong, dunno.
For reference, Slashdot uses a similar-ish system; except that it does it towards people voting up. I see “types of upvotes” problematic because often good content checks multiple boxes, but the rough idea works.
The problem with this approach is that chronological sorting leads to a lot of trash, as people know that their shitpost will be still highly visible for the others. Kind of like 4chan.