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.
I don't trust Facebook at all. But firstly, what we're building needs to be resilient to bad actors. Secondly, it's not a zero sum game, something can be beneficial for Facebook and the fediverse. Thirdly, let's be honest, no one that is currently on Mastodon is ever going to migrate to threads. And something like Threads is the only way most people would join the fediverse. You can hate Facebook and still think that Threads may be beneficial for the fediverse, they're not mutually exclusive positions.