Thanks for the point about other instances, especially if that instance does allow downvotes. I would class this as a bug in the UI / edge case the dev’s have not thought of.

Someone from somewhere else can come here and downvote just fine as well

This can’t happen actually :) When you disable downvotes for an instance, if another person downvotes it, that downvote is not accepted by us. So for an example:

• Post on Reddthat has 5 votes
• A user (user@ins.tance) on an instance with downvotes enabled, clicks downvote.
• The post on Reddthat still has 5 votes, (because we do not accept downvotes)
• The post from the user’s perspective on “ins.tance” has 4 votes.

This is part of the power of the fediverse, and all about the “Truth”-ness which is explained better here: https://reddthat.com/post/35325

Again, I’m certainly not against it and because the UI does not take that into account this would be a good reason we enable it. That coupled with the feeling of “your vote counts more” could make it worth while.
I think it was one of those things that was either the Default option, or when creating the server I looked at a few of the other ones and saw they were all leaving downvotes disabled, and left it like that too.

I’ll make another post about it and we’ll try and gauge how the community feels to see what to do.