It's not like it's an unknown little upstart. Facebook/Meta have a track record of taking as much from users as possible, and selling it. Some hesitation in giving them more seems prudent.

This is more a question of tolerance. We know Facebook is NOT tolerant of competitors, of the open web, of free software, etc. They cannot survive as a megacorp without a level of assurance and control that they can't have if they're "just another fediserver". They WILL try to wrangle control. They WILL try to eat us all up. Why let the fox in the henhouse when you already know it's a fox?

Unironically this; open web standards giving users freedom to decide who they interact with, as opposed to a closed service where the only choice is to like it or leave.

One of the key features of the Fediverse is the ability to block those instances that are toxic or annoying, so..