I agree with this decision and I don't buy the argument that this creates "a constitutionally authorized "end-run on parental authority" but I don't really get why video games are seen in a different light than a ticket to an R-rated movie or a porn magazine, both of which are legal products.
Why are video games protected by the 1st Amendment but the others not?
The others are. Motion picture ratings aren't government ratings and they aren't enforced by the government. In fact, they're not even enforced by the group that puts out the ratings, they're enforced by movie theater owners and, indirectly, by media outlets that refuse to accept advertising for movies that are either unrated or have an "adults-only" rating (formerly X, currently NC-17). The video game industry has adopted a similar rating system for games -- again, that's not a government action, that's something that is enforced by retailers.
As I understand it, Justice Scalia said that the government can't regulate violent content the same way that it regulates obscenity. Obscenity is bad, Scalia reasoned, but violence can be good. It's in Dante's Inferno
, fer cryin' out loud. Chief Justice Roberts and Justice Alito would have struck down the law for vagueness, holding out the possibility that a better-drafted law could withstand constitutional scrutiny. Justice Thomas, in dissent, essentially said that no child has any rights that an adult is bound to respect. Justice Breyer's dissent pointed out that the court should leave legislating to the legislature, which is usually Scalia's line (except when he doesn't like what the legislature did, as in this case).