Hardcore (1979)

Jake VanDorn is a businessman from the American heartland who shares strong Calvinist convictions with most of his countrymen. When his teenage daughter goes missing from her church youth convention, VanDorn hires a private investigator to find her, and the investigator spots the girl in a cheap X-rated movie. VanDorn decides to bring her back personally and during the quest he becomes familiar with the pornographic underworld.