Or maybe the problem isn’t the nipple itself, but the context in which it’s shown.
In the meme you posted, the context of the photo on the left is basically sexual assault (one person exposing another without their consent), and the meme itself implies that the (justified) reaction to it is overblown, as if it is comparable to someone willingly exposing themselves.
It is not.
The meme is a really bad take in its own right, and has nothing to do with free the nipple.
How is the meme on the right non consensual? That lady is smiling in the photo and people from Africa are not fucking idiots. They know they're being photographed for National Geographic. She clearly does not give a fuck.