I think it’s bad for society to treat adults as children, I’m happy that it should be made obviously available (there’s some merit to the argument that tech-illiterate parents often don’t know devices they give their kids have parental controls at all), but not on by default.
As bad as it is to treat adults as children, it is equally (or worse) to treat children as adults.
Parental control only get you so far. Even if we conjure the perfect tech system to manage this, remember that children were being exploited long before the internet. Bending the internet will not solve the problem, just alleviate the current flavour of child abuse, and force it back offline.