William Friedkin may be America’s most intermittently brilliant director.

His résumé includes two landmark classics (“The French Connection” and “The Exorcist”), one unjustly overlooked masterwork (“Sorcerer”), a handful of inspired entries (at a minimum I’d nominate “To Live and Die in L.A.,” “Cruising,” “Rampage” and “Bug”) and a bucket of flops (the mirthless Chevy Chase military satire “Deal of the Century” and the police thriller “Jade,” which killed David Caruso’s movie career deader than a CSI cold case).

Now 76, Friedkin began his filmmaking career in the late 1960s, an era before commerce and political correctness laid a bland, smothering hand on controversial talents.

Like his notorious contemporaries Sam Peckinpah and Ken Russell, Friedkin reveled in taking audiences to places where they would not feel comfortable.

Half a century later, he’s back at it with a vengeance. His new suspense comedy, “Killer Joe,” which opens today, grabs you by the throat and digs its claws in deep. Based on a play by Pulitzer Prize winner Tracy Letts (as was “Bug”), it’s a masterpiece of bad taste. Matthew McConaughey stars as a Dallas police detective/hit man hired by trailer-park rednecks played by Thomas Haden Church, Emile Hirsch and Gina Gershon to bump off a relative for her life insurance.

Friedkin makes the amoral tale brutally stark, brutally funny, brutally brutal. Spasms of violence, twisted sex and an aberrant act involving takeout fried chicken brought the film a rare NC-17 rating. Talking about the film by phone in July, Friedkin shrugged off the restrictive classification. He said “the three main reasons to make a movie are to move people to laughter, to tears or to fear.” In this project, he was aiming for the trifecta.

“I don’t want to see anything that isn’t risky,” he said. “I want to see things that move me in deep ways about the crooked timber of humanity. The films that interest me are about people who make absurd choices out of desperation.”

His recurring theme is “the thin line between good and evil in everyone. When I find that in a script, that’s one I want to do.”

Modern Hollywood, more interested in PG-13 fare and superheroes, has not been especially receptive, but Friedkin has stubbornly stuck to his guns.

“At every studio meeting you hear, ‘But who’s likable in this story?’ ” he groused. “If I hear that one more time I’ll break my pencil in half. I’m not interested in likability. Everyone has good and evil in them.”

Friedkin had his greatest commercial and critical successes at a time when “there were many more adult films being made. Now most of the films Hollywood makes are comic books or video games. There’s a good guy who wears Spandex and a cape and he flies around and throws thunderbolts at the villains and eradicates them. That’s the plot of almost everything that’s out there. It’s opium for the eyes.”

His movies never seem to move to a predetermined outcome you can guess in advance, even though “juvenile premises are a lot easier to make,” he said. “The films I’ve made, some are good, some are bad, but they’ve always held a mirror up to (human) nature.”

The characters in “Killer Joe” may be particularly violent and dysfunctional, but “they are not unique to that story, that film or that part of the country in East Texas,” Friedkin said. Playwright Letts developed the idea after reading a news story about a lunkhead insurance-policy murder scheme. When the time came to name the amoral clan, he christened them Smith.

“This looks to me like a metaphor for what’s going on today. What people will do for 30 pieces of silver. The Smith family is all over the country. All over the world. A guy goes out and kills a bunch of people and his neighbors say, ‘Jeez, he was a fine fellow.’ The BTK killer, the Yorkshire Ripper, everyone knew them as nice guys, sort of shy and harmless. These are the guys living in the trailer next door.”