You'd watch porn because your activity is sexually aberrational in the first place (aka sinful). Sex was left by God towards procreation, but over time, it turned into an object in itself. Even within Orthodoxy, many people believe sex is a sort of a way to become one and/or a way of obtaining pleasure from one another, yet sex was blessed within the sacrament of marriage, marriage meaning forming a family and giving birth to children. Marriage ceases to be a sacrament when people have sex only for the erotic aspect; they cease to be of spiritual use to themselves and the community and become sort of an introverted and separate unit that focuses on carnality. Carnality would be a spiritual sin (even outside of marriage, of course, since there shouldn't be "outside of marriage" to boot). Now, I know sparks will fly from me saying this. My answer, as always: to each, their own.