That’s what anime and fantasy porn is all about – pushing something to its human limits, and then going further, so the drawn representation is no longer connected to reality. The fact that it’s no longer connected to reality opens the door to a bunch of things made for people who already have this kind of disattachment from reality. It’s not just porn, either. The mistake people make is assuming there’s some “suspension of belief” in these things. There isn’t, there isn’t any belief to suspend. In a fictional world of tropes, only the tropes matter. The fact that it’s “fetish” and “comical” is built into the culture and artform itself, and from the perspective of a fan, it’s completely the wrong end of the stick to talk about “reality” or “back problems”. It’s a different world for them – a 2D world where *anything* can happen. Images and tropes have overtaken reality in that artform. You see it with MLP porn, furry porn, cringey Harry Potter fanfiction, etc. “Back problems” are about as relevant as pointing out that none of the heroes ever go to take a shit in a Marvel movie.

This is why some researchers on Japanese fan culture say that the people and situations depicted represent *other fantastical images*, not merely a caricature of reality. It’s the difference between, say, a TV sitcom where the writers hold things roughly believable, to sci-fi movies, to something like an inside joke that only people already in the culture will understand (think of those “surreal” memes, or any popular inside joke).