Santorum is an idiot, but his ideas about pornography do point to real issues.
The issue of porn is not an just an issue of freedom of speech or even of morality. Even though the porn industry is supposed to be heavily regulated, outside of income tax laws, virtually nothing gets enforced. Porn remains the largest repository of exotic STDs in the USA. Even the AIDS testing of American porn stars is not properly conducted. In addition, it is a fact that since commercial sexual material became widely available, Western sexual practices have been gradually changing.
None of this has much to do with Santorum, who is making it a Christian issue. But the idea that porn is strictly a personal choice and does not impact public life is wrong. And if politicians, particularly in California, were willing to deal with these issues, Santirum would not be able to monopolize the debate in the way he has.
Porn does have a social influence. Unfortunately, the only people willing to talk about this in public are right-wing Christians nuts and some social critics interested in gender-based critique. None of this goes anywhere. Porn is a taboo topic. The Right gets around it by making it a moral issue and the Left does the same thing by appealing to some sort of libertarian principle. And as a result, the porn industry remains the largest unregulated industry in the modern world.