Aristotle begins The Politics not with a single individual, but with a description of a man and a woman together in the family, without which the rest of society cannot exist. A healthy family is posited upon the proper and exclusive sexual relationship between a husband and wife. The family alone is capable of providing the necessary stability for the profound relationship which sexual union both symbolizes and cements and for the welfare of the children that issue from it. Violations of chastity undermine not only the family, but society as a whole. That is why chastity may be spoken of as the first political principle.
Nothing so undermines the marital sexual bond as does pornography.
Pornography isolates the physical act of sex, and its pleasure, from reality by making it an object of observation. Sex, as John Wayne once put it, is not a spectator sport. Making sex a spectacle sensationalizes it and severs it from its proper unitive and procreative context. Pornography makes the part into the whole and the means into the end. They are sterile.