It seems to me a much better way would be to require porn sites to check for an HTTP header that says the user is underage, and to require major consumer OS ven

It seems to me a much better way would be to require porn sites to check for an HTTP header that says the user is underage, and to require major consumer OS vendors to implement it. There are minimal privacy implications; it could also be applied to privacy laws and the like protecting minors; it would be trivial for sites to comply.