People raise a good point that in countries where political dissent can actually be dangerous, this would very much dissuade people from voting on things they believe in, or even coming anywhere near Lemmy period.
A better approach I think would be to have the user's host instance save their votes (the database obviously needs to remember what you voted on), but when federating those votes with other instances just hand over a cumulative total, e.g., "here on vlemmy.net we have +18 votes for this comment", which the other instances can then add. There's no need to send user information with that data.
The only official way is for the admin of your instance to defederate from the instance you want blocked, but that affects every registered user on your instance, even if they're against the action.
I just released a user script that lets you block instances yourself on the client-side as a regular user - basically just removes post and comments from the HTML if they match your block list.
Fair point. Though if nothing else stripping out usernames from vote counts would maybe save some bandwidth or database queries for the instance.