One other work it makes me think of, at least partly, is the Alan Moore/Eddie Campbell graphic novel "From Hell." It's not my favorite work, but there are a few instances of explicit sex in it that are properly woven into the story.
Perhaps there was a medium-specific argument in what JCM was doing: in a literary fiction, when the characters have sex, it's real sex within this fictional world. Cinema however has the particular feature of being able to break through pure make-believe and go into the actual world. I don't want to bring the whole photo-is-real-is-not-shut-up-no-you-shut-up bickering, but suffice it to say that the way we make movies (or photo), we can represent actually happening acts, and that's where it's unsettling and powerful. (Of course there is also simulation in cinema, but everyone already knew that...)