The people who are sexually aroused by children and are willing to physically act on that arousal would do so whether or not any pornography had ever been available to them. To those people, a public beach is every bit the instrument of arousal that, for example, a cartoon drawing of a child engaged in sexual acts is. But the logic leap required to believe that someone without a previous inclination towards children would suddenly be driven to commit a physical act against a child when exposed to pornography is just laughable, IMHO.