@gamingonlinux Agreed. Some people are really enraged with the idea that Meta is using information they post publicly (which they probably would do anyway, federation or otherwise).
Although, for my instance, a lot of it was about difficulty moderating comments. Meta is (supposedly) notoriously bad about controlling malicious content. Presumably mods on my instance don't want to constantly have to deal with people from Threads. If they block other instances which don't moderate, it doesn't make sense to allow Threads just because they're "important".
There's also the reverse - I'm on a nsfw friendly instance, and I assume Threads will block instances like that as a matter of policy. As well as any other instances which don't meet their "community guidelines".
That being said, even though I do like Mastodon and the Fediverse, there is a bit too much focus on instance admins that have unilateral control over what you do and don't consume.
Apologies for the long rant, guess I feel strongly about this stuff.