Bret Easton Ellis said this quote
“ The audience-- the book's actual cast-- quickly realized what had happened. The reason the movie dropped everything that made the novel real was because there was no way the parents who ran the studio would ever expose their children in the same black light the book did. The movie was begging for our sympathy whereas the book didn't give a shit. And attitudes about drugs and sex had shifted quickly from 1985 to 1987 (and a regime change at the studio didn't help) so the source material-- surprisingly conservative despite its surface immorality-- had to be reshaped. ”