It doesn't, in the same way porn doesn't. Of course, as with that, it's debatable, but basically it's not so simple as "freedom of speech! you can't do that!", because if it was actually like that, you'd be able to do stuff like shout fire in a theater and such. That's not saying I support it though..
That's not true, actually. The phrase comes from a Supreme Court decision that "speech which serves no conceivable useful purpose and is extremely and imminently dangerous so that resort to the courts or administrative procedures is not practical and expresses the permissible limitations on free speech consistent with the terms of the First Amendment of the United States Constitution." So, no, you can't. It's illegal. Lrn2education.
Please tell me how this does. They aren't censoring videogames just prohibiting it to minors. It's perfectly legal within the constitution. Most large retailers will enforce the law, if it gets passed, simply because they'll be the ones held accountable. That's unfortunate because it's taking even more responsibility from the parents, when the opposite should occur. Parents need to be responsible for making sure their child is responsible for themselves. What'll end up happening is some angry teen does something stupid at school. The school phones the parent asking how this happened. Meanwhile the police arrive, because whenever a kid gets angry at school it's going to be a columbine. So, the police are there, the school's looking into it and that puts so much pressure on the parent that instead of admitting they failed and their child is a ****-up, they're going to blame videogames. After that, large rallies across the nation will spring up burning videogames in huge bonfires. Most of the Bungie crew will escape to Japan, Activision will burn to the ground, EA will hide behind the face of Madden, and Shiska will burn at the stake.