Breyer's dissent has a bit of nice reasoning in it, actually.
"But what sense does it make
to forbid selling to a 13-year-old boy a magazine with an
image of a nude woman, while protecting a sale to that 13
year-old of an interactive video game in which he actively,
but virtually, binds and gags the woman, then tortures
and kills her? What kind of First Amendment would
permit the government to protect children by restrict-
ing sales of that extremely violent video game only when
the woman—bound, gagged, tortured, and killed—is also
This anomaly is not compelled by the First Amendment.
It disappears once one recognizes that extreme violence,
where interactive, and without literary, artistic, or similar
justification, can prove at least as, if not more, harmful to
children as photographs of nudity. And the record here is
more than adequate to support such a view. That is why I
believe that Ginsberg controls the outcome here a fortiori.
And it is why I believe California’s law is constitutional on
Basically, the court had previously ruled that it's ok to ban porn sales to children, and the court is generally bound to prior rulings unless overturned by new legislation. The logic used to ban pornography sales to kids still applies to this case.
Not saying it's a good law, but Breyer's position makes a lot of sense.