While this will probably not be a surprise, I want to be clear that the Mastodon instance I maintain, techpolicy.social, will absolutely be federating with and not blocking Threads. I'm a big fan of their embrace of federation (and also, a happy Threads user, where I've found some additional pieces of what I loved about Twitter that haven't quite reached Mastodon or Bluesky).
However if any of my local users disagrees with that decision, I'd be happy to discuss the matter - here or in realtime.