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.
Facebook is reported to be using a shadow profile of non-facebook users. Mastodon stated that whenever you interact with a Threads user it will be recorded by Facebook. All they have to do is join a conversation as a lurker, and your data is sent to Facebook. Given a few more points such as time of day and topic they can start to narrow downwho you are. Add your profile picture, and manner of speech an AI, which they have a multitude of, can generate a probability of who is communicating. Over numerous interactions the law of six degrees of separation will have you nailed down. In some countries this is potentially a problem over data retention, but they'll have lawyers looking night and day for a way around those trifling laws. Willingness to federate might be seen as consent by default in some cases.
This highlights my point. This attack vector exists with or without threads. Facebook and friends can already scrape fediverse posts and map them to users. Defederating Meta instances won't solve this vulnerability. Which is my point, people don't understand the actual risks.
Data gained through integration of an instance is far more than what's gained in scraping. The data gained through federation will no doubt increase as Meta adds new features that require more data in order to federate with them. They have over a decade of evidence showing us they're evil and have no respect for privacy or people. I do not understand your logic in saying it's okay to federate, it's like watching somebody defend an abusive partner. They've hurt you and communities in the past, stop giving them more rope. The devil does not need an advocate.