If it was almost any other corporation I'd be willing to give them a chance. If Tumblr actually launches ActivityPub I doubt many people will complain. The fact that it's Facebook though makes it pretty much a non-starter imo.
As an admin of a small instance, the privacy stuff is pretty secondary to the moderation headache Threads' traffic would surely induce. mastodon.social by itself produces enough crap that I've silenced them, I can't imagine that Threads will be any better and indeed assume it'll be much worse in that regard.
Besides that, I think there's a difference between having data publicly available and voluntarily sending it straight to a data broker. Either way I don't think you should need much of a reason to tell Facebook to fuck off and I find it kind of strange that people seem so hesitant about it ¯\_(ツ)_/¯
These days they don't even like each other
https://www.nytimes.com/2023/11/30/arts/music/hall-oates-lawsuit.html