That's exactly what the legislation constrains - Zuck's select * from where user_id = 'technofiend' returns 3 rows not hundreds or thousands, or zero if I've opted out of data collection entirely.

You can't simply throw your hands up and say "Well Facebook has a billion users too bad so sad if they collect data you don't like" because there are in fact plenty of laws elsewhere that restrict their activity. It's entirely possibly to tell them to keep their grubby hands of my bits and their cookies out of my browser. And yes if that means I have to pay for sites I use for free now, so be it. I can't help but think that'll drive content towards quality anyway.

Yes, there are laws restricting how and when data can be processed.

That someone has the ability to do something bad does not mean they cannot be restricted from doing it by the law.

That this sort of restriction is largely missing from US data laws is one reason we see so much fuss about data centre locations and 'safe harbour' provisions.