Yep this is exactly right. Too many people are unaware that their votes are not anonymous on Lemmy and blocking the public tool only helps the bad guys who already know this. I’ve always thought this was a major weakness in Lemmy but I don’t have a solution myself without some other major drawback.
I think probably votes should be anonymized or batched between servers so that only your instance’s admins can see individual votes and you just have to trust the instances you federate with that they aren’t pulling any shenanigans or otherwise defederate. That’s not an easy problem to solve, but it’s not like it’s not currently possible to manipulate votes with a federated server, it would just be harder to detect. Regardless I think the need for privacy wins here.
It’s not exactly clear what the main goal is here and it sounds like a bad idea on first glance after reading your last paragraph. But it sounds like you might be looking for mandatory profiles.
https://learn.microsoft.com/en-us/windows/client-management/client-tools/mandatory-user-profile
But now that I read it again I think you might be conflating users/profiles with sessions. In which case no, this is neither possible nor a good idea. But it still might be okay with mandatory profiles if the device and app works the same from multiple sessions.
Anyway, you might get better answers if you state the full problem, including details on software and device, not just your proposed solution.
https://xyproblem.info/