Edit: obligatory explanation (thanks mods for squaring me away)…
What you see via the UI isn’t “all that exists”. Unlike Reddit, where everything is a black box, there are a lot more eyeballs who can see “under the hood”. Any instance admin, proper or rogue, gets a ton of information that users won’t normally see. The attached example demonstrates that while users will only see upvote/downvote tallies, admins can see who actually performed those actions.
Edit: To clarify, not just YOUR instance admin gets this info. This is ANY instance admin across the Fediverse.
I agree with you about harassment issues, and the importance of controlling the transfer of admin-level data between instances, but for your last scenario, doesn’t blocking only apply to users who are logged in? Assuming your hypothetical tankies and Nazis were actually posting as well as blocking, it would be easy to find them just by logging out, and there are a lot of ways to get them banned or otherwise counteract their activities that don’t require someone to interact directly with them while logged in. The case you’re describing is not the kind of situation where the most important action is to argue with them. Arguing with extremists usually just validates their delusions, and encourages them to keep doing what they’re doing.