Starring Amanda Seyfried and Peter Sarsgaard. Rated 18A.

Codirectors Rob Epstein and Jeffrey Friedman have been responsible for such important documentaries as The Celluloid Closet and The Times of Harvey Milk. Their first narrative film, Howl, took an uneven, multimedia approach to poet Allen Ginsberg’s dance with literary censorship. So it’s even harder to grasp what they were going for in this conventional and remarkably incurious telling of the Linda Lovelace saga.

For some reason, Amanda Seyfried was chosen to play Lovelace, whose appeal in the Nixonian ’70s was her embodiment of the (oddly talented) girl next door. But in dark hair and freckles, the big-eyed Les Miz moppet manages to disappear into the role and emerge as the movie’s strongest asset. Also good is Peter Sarsgaard as Chuck Traynor, the aptly named Svengali who turned Florida’s suburban Linda Boreman into the most famous porn star ever.

Between the porntastic ’staches and butterfly collars, plus the usual proto-disco music cues, everyone revels in the Boogie Nights details. Hank Azaria, Bobby Cannavale, and Chris Noth have fun, and Adam Brody plays Lovelace’s happy Deep Throat costar, Harry Reems, whose character discovers a clitoris down her esophagus.

Casting hits a snag when cocky Howl star James Franco shows up as Hugh Hefner, already a craggy, middle-aged dude in 1972. And a brief glimpse of Eric Roberts reminds us of the superior Star 80, about a creepy manipulator even worse than Chuck Traynor. The new movie seems afraid to truly engage in the awful experiences described by Boreman in her 1980 book, Ordeal, and is also unwilling to confront her many contradictions, which persisted when she became an antiporn activist.

The filmmakers instead prefer to have all complexities explained by the religion-coated self-loathing of Linda’s mother, played by someone else you wouldn’t expect to find in this kind of role: Sharon Stone.