A sender cannot shield a message posted to a discussion group. But they cannot prevent a minor from visiting. The upshot is that if the anti-indecency provision is really to be enforced, the government will have to closely police cyberspace and impose ex post facto law, in the sense that we often won't know whether a text is indecent until the authorities tell us. This is a monstrous situation in a society that prides itself on its freedom. One would think that proponents of a strong family would not look to government for protection.
Paternalism is the kiss of death.
It implies that the family cannot sustain itself without the intrusion of the state. Ask government to protect you from indecency and it will find all kinds of things indecent. Once the state has its foot in the door, it's too late. Once we extend the principle to political ideas, you can say good-bye to free debate. The irony of all this is that, as usual, the marketplace is already providing assistance to parents who are reasonably concerned with what their children may encounter in cyberspace.