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)