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.
This was my thoughts as well. I understand the need for an audit trail.
Would be very easy to build up an interaction graph with this data that could be used for fingerprinting. If this is an issue for you, though, just browse without signing in/interacting
Was just thinking about this more though, and unfortunately there can also be rogue instances that allow bot users to be created and interact with other instances posts, so this issue could still persist.
Could replace the usernames with UUIDs, and keep the username-UUID map back on the source instance? Then you get an audit trail, but not associated with user identity. There’s also no guarantee that people don’t use bob_jones as their username, and this is Personally Identifiable Information, which brings up some GDPR stuff too.
The problem with that is that every interaction that any user has with a post or a comment would require calls back to the home instance in order to lookup those usernames. That’s a LOT of extra load
There is no reason you couldn’t only do it for votes and not for posts and comments.