The arguments I've heard about tracking etc are misguided and don't understand the actual risks.
Firstly, posts on the fediverse are already likely being consumed by advertising platforms like Facebook & Google. It would be trivial for big tech companies to setup relays that act as scrapers.
Secondly, the value in platform's tracking individuals is for advertising. There is no mechanism for these platforms to identify you browsing the we if your instance federated with threads. Your instance won't share cookie sessions etc with threads. It doesn't increase your exposure.
Thirdly, these platforms have the know how to deal with spam and they will be incentivised to share that tech with other federated instances.
Don't get me wrong, Facebook is an evil company. But I haven't heard a decent argument as to why them joining the fediverse is a bad thing. We always have the option to defederate in the future.
Change my mind.
The beauty of federating servers is that everybody can setup their own server, provided they own a domain name.
In theory I could start a server registered to unanimousstargazer.social and create an account called @unanimousstargazer@unanimousstargazer.social and participate in the fediverse. If I choose to block Meta, then that's my choice.
I agree people are unnecessarily making a fuzz about this, as it's their own choice to join a server or not. The fediverse is open, so why can't Meta join. That's up to them. And if I want to block them, that's up to me.