The steelman argument is that parents are not necessarily up to date on the technology, and cannot reasonably be expected to supervise teenagers 24/7 up to the age of 18. Compare movie ratings or alcohol laws, for example: there's a non-parental obligation on third parties not to provide alcohol to children or let them in to R18 showings.

But the implementation matters, and almost all of these bills internationally are being done in bad faith by coordinated big-money groups against technologically illiterate and reactionary populist governments.

(if we really want to get into an argument, there's what the UK calls "Gillick competence": the ability of children to seek medical treatment without the knowledge and against the will of their parents)

In the UK parents can give children alcohol below the age of 18. parents get to make the final decision at home so I do not think its really comparable.

I would personally favour allowing parents to buy drinks for children below the current limits (18 without a meal, 16 for wine, beer and cider with a meal).

The alternative to this is empowering parents by regulating SIM cards (child safe cards already exist) and allowing parents to control internet connectivity either through the ISP or at the router - far better than regulating general purpose devices. The devices come with sensible defaults that parents can change.

That steelman still stands on a core assumption that its both the state's responsibility and right to step in and parent on everyone's behalf.

Maybe a majority of people today agree with that, but I know I don't and I never hear that assumption debated directly.