Thinking in less moralistic, more utilitarian terms, I would think that romance novels and "wholesome culture" provide the real comparative problems. People see "happily married couples" in popular culture and wonder why their marriage doesn't work as well. They become unhappy and dissatisfied, rather than learning to deal with their problems.
Porn, at worst, makes you think your partner is fat, blemished, and ugly. Either sophisticated intellect or raw animal desire (but which one? can both work, or do they operate against each other?) can get you over that hurdle. But what is to get one over being "a marital purist"? After all, to think a marriage can be perfect feels like such a noble sentiment.
Maybe porn (of all things) plays a positive role here. It convinces its viewers that desire is invariably laden with ambiguities and contradictions. Might even the stupid porn users be capable of picking this up?