As an aside, I know a photographer who shoots nudes and incorporates sexual activity into the scenarios, and he has done a lot of exploration into the idea of the boundaries - about how, as a man, he has formed social expectations about how far he's expected to push things with women, what happens when he doesn't act on it, and how that changes the interaction between model and photographer.
Most of his images are about female self-sexuality, so he's literally not part of the picture, and a lot of his effort, when creating the images, goes into providing the space for the women to be free in their self-expression. He has to establish a bond where they know he will not take advantage, even on a psychic level, so to speak.
(He's also done work with men, and challenged himself on assumptions and reactions that he has about same-sex eroticism.)
So in my eyes, it's entirely possible for someone to explore the sexual boundaries of the model-photographer relationship without it descending into potential abuse. And even if the photographer wanted to place themselves into the centre of the action, some careful thought could produce interesting imagery without sacrificing either the erotic side of things or a sense of respect for people.
But taking advantage of people in the course of creating your work shows no imagination at all. Just because you can, doesn't mean you should - and if you are, it's a sign that you're not working hard enough at what really matters.
