In the latter case, I think it might be feasible to prevent upvotes from being counted multiple times if the username is identical on different instances, since upvotes are public. Is there already a mechanism to do this?
If @dude@lemmy.world upvotes and @dude@lemmy.ml downvotes, how do we decide which is the canonical vote? How can we say for sure they're even run by the same user?
Also, isn’t it much more common in the Fediverse than on central platforms for the same user to have multiple accounts with different usernames?
This was the norm on Reddit too.
I suppose this would only be possible if the different instances would log IP addresses and share this information with other instances. That doesn’t seem desirable to me at all, and probably wouldn’t be legal, at least in Europe, because of the GDPR. Are there other possibilities? Cookies?
Let's not inundate the fediverse with tracking cookies and privacy invasion.
I get where you're coming from, but I just think that the solutions to these problems aren't actually solutions, and they're a case where the cure is worse than the ailment.