Sorry, but you are not correct on many levels.
Art is not some fancy word to throw out like that. NSFW are really depends on the circumstances, like what you showcase and where you post it. I also think that some nsfw takes things a little too far though where it moves out of art and into just something completely inappropriate, which also only really belongs in certain places away from minors. I won't talk about that too much, but I'll just say that it's somewhat disturbing to me - even as an adult and I would never, as a game developer create such a story. It's also unprofessional, unwise. Although, one thing I agree with you is that the developer should be free to make this, because in the end, it's about what is he trying to showcase and if it works for him. So far, I see that lot's of people, like me, don't give a good feedback and it's not about the NSFW content, rather how it is handled.