I agree with this approach but there's an issue with "it's their job, they know best". They will inevitably want to put the same tracking crap in the logged-in

I agree with this approach but there's an issue with "it's their job, they know best". They will inevitably want to put the same tracking crap in the logged-in site as well, so they can see how visitors converted into users, how they used the site once they were users, how valuable that made them as customers, and so on. As long as FB/other analytics firm is saying "we can help you market better with additional data", marketers are going to advocate sharing it.