I agree with you that parents need to ultimately be responsible for keeping their kids off social media. I think there are a few problems here:

- Social media is still somewhat new, and the broader public is only now discovering that it's a clear net negative both personally and for society. Because this is such a new realization, I think a LOT of people have not really figured out how this problem should be dealt with. (both personally, via social norms, but also with regard to laws and regulations.

- No matter how awesome of a parent you are, 100% of your kids friends will have social media and they will introduce it to you kid. That may do less harm than if they have it themselves, but some harm will still be done.

- There are network effects to consider. It's true that it's your personal fault if you use cocaine -- however we also understand that cocaine is so addictive that it really cannot be used safely. Social media is metaphorically the same. It's a personal failing if you're a social media addict, however broadly almost everyone is susceptible to it. In my mind, that is an argument for regulation.

Now that said, I have zero faith that our government can actually build sensible regulation here.