Why did Michelle Phiffer turn down the role?

The subject matter was quite dark, gritty, and uber edgy for the time.

I mean - aside from the LGBT controversy in a time of AIDs - getting splooge thrown at your face has never been a "thing" in the history of mainstream American cinema. That kind of stuff might happen as a punchline in a modern R-rated comedy or in some experimental Euro romp.

Should TSOTL have flopped with a trite story, terrible acting from Hopkins, etc. it could have humiliated Pfeiffer, making her the butt of jokes a la Elizabeth Berkley in "Showgirls."

The chemistry between Hopkins and Foster, along with the lingering, extreme close-ups - and how both actors negotiate said close-ups - are everything to Demme.

Plus, I don't think this role was entirely aligned with Pfeiffer's image and branding; IMHO without Foster to play off of Hopkins, Silence would not have been the same "intense" thriller it is.

Foster sometimes tends to pick projects in which her main character could easily be a man instead of a woman ("Flightplan," "Panic Room," "The Brave One,") and, were it not for the source material, Starling could have been written as a male character; who's to say, despite the tonal differences, that it would not have been an equally effective movie? "In the Company of Men," is one of my favourite movies ever, and it has sharp commentary on how men behave in the world pitted against each other.

Aside from scheduling conflicts or salary concerns, I think Pfeiffer had her own career trajectory / ascension, and this project was seen as too risky.

She thought it was too violent and too risky I believe. Foster was a fan of the book and had just won an oscar for what was perhaps one of the most controversial mainstream film of the 80s. She was all for it and fought for it and won the role.