I don't see the problem. He's offering a completely legal product to an eager audience. If people want to propose banning social media in some capacity, that could and should be voted on-- but Zuck isn't violating any legal or moral law I've ever heard of, and he shouldn't have to guess what products will be illegal in 20 years and preemptively withdraw them.
If it's harming your mental health, stop using it. The "Delete App" button is right there.