In Requiem for a Dream, one of the most famous scenes is of the female lead and an unnamed other girl going "ass to ass" with a double-ended dildo in front of a crowd of men in a sleazy strip club for heroin money. While the scene is very sexual, it isn't even remotely sexy. Everything is grimey, dirty, the two girls look horrified and miserable, the men are acting feral, aggressive and totally uncaring, one guy shoves a wad of cash in the girl's mouth. It's an ugly, disgusting, upsetting unsexy scene and it's meant to be, and it works perfectly.
What you don't see in the scene is extended closeups of their ass and tits, sexy glamour shots or erotic moaning. It isn't filmed like a porn scene. That's why it works. Compare that to Cuties, which makes everything look pretty and zooms in on the little girls' asses every five seconds and treats the material as more funny/quirky than horrifying, and you see the problem.