That "soul" element is where religion stakes its claim on the porn question. Now, sexuality is a loaded issue. Many Christian traditions say sex must only be experienced within heterosexual marriage. Progressive Christians tend to be more lenient, and to argue that sexuality within the bounds of a loving and respectful relationship is no sin. But we can go further than simply absolving consensual sex of sinfulness: Rowan Williams, prior to his becoming Archbishop of Canterbury, actually gave a ground-breaking lecture, "The Body's Grace," on why sexuality is a spiritual—even a Christian—good, and how that bodily grace is not simply limited to those in a male-female marriage. "Grace," Williams writes, "for the Christian believer, is a transformation that depends in large part on knowing yourself to be seen in a certain way: as significant, as wanted." And it is human sexuality—as a part of a relationship between two people, not one person and pornographic images—that offers us this foretaste of divine love.
The incessant use of pornography removes another person from the equation. Instead of 1+1 equaling so much more than one, with porn we end up with 1+0, which somehow equals zero. This is the math dramatically suggested in the film by the character of Esther (Julianne Moore), a woman who doesn't fit Jon's superficial standards of beauty—a woman who is vulnerable, ghostly, and truly beautiful as she calls him to a higher and better way of being human—and of being a Child of God.
Set aside for the moment—if you somehow can—the emotional damage to individuals, to their relationships, to their attitudes that comes from constantly consuming unrealistic and objectifying images of human beings having sex. Jon's choice of pornography as his highest good is worthy of weekly confession because instead of offering the body's grace—that taste of loving connection which in turn directs us back toward the Author of all grace, joy, and beauty—pornography leads back only into ourselves. Because of that spiritually-closed circle, that narcissism, pornography should be condemned by all Christians, not simply the moralists. (And all pornography ought to be called out for censure; maybe sex is not your particular weakness, but what about food porn, travel porn, celebrity porn?)
"To love another person / Is to see the face of God," is the final conclusion of Les Misérables. I think it is also the final conclusion of Don Jon. Go see the film and see what you think.