this is the real problem. Mastodon and lemmy share way more information than they actually need to (like lemmy shares a list of usernames who upvoted or downvoted a post, not just a count), and if you're using one of those services you should expect that all your data and interactions are public. that's the actual threat here, not the possibility that facebook might suck up that data. Blocking Threads from federating is just a short-term patch over mastodon's bad privacy controls.