The reason is that the key to democracy is not free choice. As we know from the Weimar Republic, people can freely choose anything, even Hitler. The key, as our Founding Fathers knew, is virtue. Only a virtuous person is capable of rational consent because only a virtuous person's reason is unclouded by the habitual rationalizations of vice. Vice inevitably infects the faculty of judgment. No matter how democratic their institutions, morally enervated people cannot be free. And people who are enslaved to their passions inevitably become slaves to tyrants. Thus, our Founders predicated the success of democracy in America upon the virtue of the American people.
The insidiousness of pornography is not just that it is sinful and therefore clouds a person's judgement.
There's a biochemical aspect of it that makes it addictive, and therefore enslaving. There are lots of immoral writings out there, but they do not wreak havoc like porn, because people do not develop a biochemical pleasure from it.
