And Al Pacino was in this because why?

It looked good on paper? The great Friedkin was directing? Looked like a box-office hit? Maybe all of those things, but wouldn't an actor of his stature refrain from a film that seemed..expolitive or borderline sleaze? Yes, I know it'a a film ABOUT the sleaze,but it still is what it is.
For example, if Friedkin soley wanted a character study, he didn't have to show the sleaze, but speak of it in the narrative.
Or of Freidkin thought it would be abother "shocker" like The Exorcist, he was about a decade too late, except for those living in a naive existence(well, on 2nd thought, maybe Friedkin was right about that part)