I would expect a "man" in your position to possess a greater understanding of sexual provocation. Why should a nipple matter when every other part of the woman is completely naked? You do not need to show nipples, vaginas or fucking sphincters for a photograph to be inappropriate. A good photographer, can convey a deep sexual theme with a model that is fully clothed.
Yours is certainly not good photography. It is closer to "let's see how far I can get this camera up this young girls arse." That is not art, it's a creepy guy who never left puberty living out his teen fantasy of taking pictures of young naked women.
The second half of your comment is inaccurate and irrelevant to this issue. It is legalized prostitution that has the effects you are talking about, but legalizing sex as commerce between adults has absolutely nothing to do with subjecting very young girls to images that show women portraying themselves as a selection of holes for men to do with what they please.
That may be appropriate on Facebook and Instagram, and perhaps that's why I do not use Facebook or Instagram. This hypersexualization of children does the opposite of all the bullshit you're trying to use as an excuse for your actions. I can tell you really believe it though.
You believe this bullshit because you have to, it makes you feel better about the role you are playing in corrupting the youth of today. Perhaps one day, when you have matured to a point where you no longer feel the need to base your entire life and career on seeing the next pair of tits, then you will be able to stop and consider the psychological effects that your work has on young girls-- and boys.
Now, you have wasted enough of my time so I am muting you.