i think that the control exists in, and only in, the hands of parents.
such 'laws' are just going to create black markets which is going to increase the violence involved.
it didn't work for alcohol, it didn't work for drugs, why would it work for pictures.
not only that, if you can justify banning one kind of picture you can stretch it to banning other kinds of pictures, and that doesn't really go anywhere good either.
censorship and monopoly claims are immoral.
parents should a) not allow what they don't want their children to see, and b) not be forced to socialise their children with other children whose parents have no morals.