Directed by Oscar winner William Friedkin, "Killer Joe" is only the second NC-17 theatrical film to be released in the U.S. this year, because no one under 18 can be admitted no matter who accompanies them and limited audiences mean limited revenues.
Still, more and more of Hollywood's top talent like McConaughey, Friedkin, and co-stars Emile Hirsch, Gina Gershon and Thomas Haden Church are embracing edgy projects that require the stiff rating.
Oscar-winning actress Juliette Binoche starred in the NC-17-rated French film "Elles," released earlier this year. "X-Men: First Class" and "Inglourious Basterds" star Michael Fassbender won raves for his turn as a sex addict in last year's only theatrically released NC-17-rated film, "Shame."
"The NC-17 rating is about to go mainstream," said box-office analyst Paul Dergarabedian of Hollywood.com. "If Matthew McConaughey and Michael Fassbender are giving their stamp of approval to the creative freedom that NC-17 allows, people might go for it. While it may affect the ability to market a film, it brings a whole new cache of subversive marketing, and mainstream actors who give it legitimacy, credibility and raise it to a whole new level.
"Let's wear it as a badge and keep it shined!" McConaughey said of the NC-17 rating for "Killer Joe."
The MPAA says on its website that an NC-17-rated film "is one that, in the view of the Rating Board, most parents would consider patently too adult for their children 17 and under."
That's certainly true of "Killer Joe," which opens in New York on Friday and other major cities next week. The MPAA says it contains "graphic disturbing content involving violence and sexuality, and a scene of brutality."
Adapted from the stage by Pulitzer Prize-winning playwright Tracy Letts, it's a story about a small-time drug dealer (Hirsch) who hires a cop moonlighting as a hit-man (McConaughey) to kill his mother for her life-insurance benefits, and offers his virgin sister as collateral. It's adult material.
Still, Friedkin was prepared to edit the film to potentially qualify for an R-rating, "but they wanted to go so far" with the cuts.
"I often say what (the MPAA) wanted to do is what the generals said we had to do in Vietnam, which was destroy the country in order to save it," said the director, who won an Oscar for 1971's "The French Connection" and an Oscar nomination for 1973's "The Exorcist."
"We're not targeting a teenage audience, so it's the correct rating," Friedkin continued. "But there are other films that I think are far more graphic in every way—language, sex and violence—that are playing with an R, because you won't see an NC-17—which is an 'X' really—on a major studio film."
McConaughey, who has been breaking out of his broad rom-com appeal with edgier roles, described "Killer Joe" as "a wild, raunchy, cheerfully amoral piece."
"It was a character I hadn't played before," he said of gentlemanly cop/contract killer Joe Cooper. "It was a character I didn't know how to do right away."
The disturbing and darkly funny story with themes of loyalty and vengeance didn't appeal to him right away, either.
"When I first read the thing, I didn't like it. I didn't think it was funny. I was disgusted by it," the actor said. "But then I clicked into my funny-bone side of it and I was like, 'I get it. I get that this is absurd and funny, and it's OK.'"
Friedkin says the appeal of the story lies in the desperation of its characters.
"I found it fascinating because at the heart of it, at the crux of it, is small time criminality—the desperate ends that people will go to who find themselves trapped in their own skin and by their own dreams," he said. "All these people have big dreams and they don't know how to accomplish them, and they think that murder is the answer."
He drew comparisons to the real-life cases of O.J. Simpson, Robert Blake and Casey Anthony.
A dark tale like "Killer Joe" will find an audience, Friedkin said, no matter its rating.
"Somebody's going to see these films, and they're gonna like them or hate them. Sometimes they'll be memorable. Often they'll be challenging. And I enjoy doing that," he said. "I don't have any respect for someone who sets out to do a blockbuster. I just really don't. I think that's just a crass, commercial approach."
Films rated NC-17 are rarely commercial. Pedro Almodovar's 2004 film "Bad Education" has the highest box-office tally of any NC-17 film with just over $5 million.
"An NC-17 movie is never going to be about box office," Dergarabedian said. "It's always going to be about creative freedom. That's the best thing about the NC-17."
AP Entertainment Writer Sandy Cohen is on Twitter: www.twitter.com/APSandy.