I've thought a lot about this work over the years.
I too see a progression here that's alien to our sense of the" proper". But it's too easy to just write the whole thing off as sensationalism, opportunism.

I have some personal and family experience with this area of human existence, and am not sure my wife wants to share it, so will hold my peace till I know.
But, like so many stories that, in the end, are seen to offend against propriety and righteousness, the story is bigger.  

Capitalism searches out the darkest corners of human potential, and mainlines them.