If nudity is necessary to the story - in my experience, it rarely is - I would not object. The more objectifying and gratuitous the nudity is, the stronger my objection becomes, much the same as with violence in film. One can not have a film about war without violence; one can most definitely have a film about war with gratuitous and unrealistic violence.
Think of The Passion of the Christ: too much violence? I do not think so. Gangs of New York? I do not think so either. Many films depict less violence than either, with the violence depicted being yet more gratuitous. Now, the recent remake of Judge Dredd is likely the most gratuitously gory and violent picture ever made, or the disgustingly-meaningless, pointless full-frontal male trans-sexual nudity in The Hangover 3.
The same story could always be told without nudity or violence respectively, but, in doing so, is stripped of much of its power. Think of a continuum, here, with American Beauty at one end (art), with many sex scenes in the middle (part for the story, part for the titillation), and with pornography at the far end (regardless of Stoya’s protestations, no story or meaning, just titillation).
Now, Ed’s view strikes me as far too extreme. Especially in writing, if you gut the story of foul language, sex, violence, dirty humour, psychological weirdness, and the various other foibles of human existence, taking the same process to an extreme degree, would reduce a 400-page novel to a single-page synopsis. That’s not to say torrid romance novels are art; there is some distinction here, which we denote with the word “art”, a distinction that is not only aesthetic, but also symbolical, and even ethical.
Whether a scene of nudity or violence, imaged or written, takes place in the context devoid of meaning, or with a meaning inimical to virtue, it is not art. It makes no statements. When a scene of nudity or violence is contextualized in a certain way, it can become art. It can make a statement in a direct or symbolical way, and with great emotional force.
Think of the nude scene with the girl standing in the window in the aforementioned American Beauty; the film-maker and actress use the nudity as a window to something more, as a symbol, as a means, not an end. Now, think of the same exact scene, transposed to “sexting”, and nothing else. It is now an end in itself, devoid of symbolism or further meaning. The change of context makes it pointless, meaningless except for the purposes of titillation, and thus becomes sinful.