ID requirements in real life don't give the state and a hundred third parties the power to track every other purchase you make and every other place you visit.

You're not wrong, and there should be privacy measures in place, but if you're that concerned, just buy your porn in real life or get your porn from the millions of other websites.

Quitting your porn addiction is also a solution.

My problem is that it undermines the principles of online privacy and anonymity, and that that is its real goal.

You have to prove your age and identity and there's no way for a website to look at a picture of your ID and not know if it's fake or not or whether you're actually the person submitting that ID. A physical location has lesser restrictions because they get to see you in person and they can check your ID to see if it's fake or if the photo on the ID doesn't match the person presenting it.