Consider a fabricated, but frighteningly not-too-distant, future of 2022 America. In a “nation reborn” by “our New Founding Fathers,” unemployment barely scrapes 1% and crime has plummeted to unprecedentedly safe levels. Life, it seems, is good.

But 8,754 annual utopian hours are possible only thanks to a brutally dystopian rebranding of the remaining 12 — a time known as the Purge during which all crime, including murder, becomes legal from 7 p.m. to 7 a.m. (Of course, “Purge feeds” are televised.)

Police, fire and emergency personnel take the night off. And while targeting “Level 10” government employees or using “Class 4” weapons (unspecified, but think “leaders” and “bombs”) is prohibited, everything and everyone else is fair game.

There’s a feel-good version of this story, in which a group of otherwise timid folks put together a party powered by prostitutes and marijuana. The Purge isn’t it.

Instead, writer-director James DeMonaco’s nasty, brutish and 85-minutes-short film intelligently explodes the impetus behind the Milgram experiment to a shocking, menacing macro level: If it were not only temporarily allowed, but even encouraged, by our government, would you, as a law-abiding citizen, scratch your itch to kill?

During ironically soothing PSA ads, the Purge is described as “releasing the beast.” But what, exactly, is being purged? Our urge or our scourge, as the movie suggests, of the poor and homeless? Is this a brief moment of catharsis carved out to save our society, or is it merely a genocidal pogrom disguised as a governmental program — a socioeconomic cleansing under the guise of a “stronger” America?

Eventually, DeMonaco’s brilliant setup yields to so-so siege action that takes place in the home of James Sandin (Ethan Hawke). He’s a security-system salesman for whose family the Purge has enabled lavish luxury — fortifying his bank account and living space as much, if not more, as his neighbors’ homes.

“A garage in a boat? Who needs a car garage in a boat?,” James laughs while riding out what he thinks will be another peaceful night of wish-list shopping and movies with the family — wife Mary (Lena Headey), teen daughter Zoey (Adelaide Kane) and preteen son Charlie (Max Burkholder).

Charlie’s obsessed with secrecy, surveillance and survival — more or less all of the mysteries of the Purge he’s only just now beginning to comprehend. And lining the walls of his bedroom hidey-hole are some briefly glimpsed, somewhat disturbing drawings that shine a light on his darkest thoughts.

Like a young Joaquin Phoenix, Burkholder suggests an internal tumult and psychological complexity. And by coloring Charlie with outside-the-lines curiosity, The Purge creates a strong escape hatch from the genre’s usual clichés; why wouldn’t a kid this eager to know more about the Purge go exploring, even in the dark?

The Sandins’ well guarded home suffers various threats from within and without — some laughably unlikely, some credibly formidable, and most derived from Charlie allowing a homeless veteran inside (Edwin Hodge, credited as Bloody Stranger).

Bloody Stranger is the “filthy swine” quarry of Polite Stranger (Rhys Wakefield) and his prep school-groomed gang of marauders. He offers a simple bargain from the Sandins’ doorstep: Let Bloody Stranger out so they can finish the job … or they’ll huff, puff and blow the house in.

Flashing an unsettling rictus grin at the Sandins’ security camera — meaning us — Wakefield oozes entitled menace in a manner that approaches Christian Bale’s as Patrick Bateman in American Psycho. Wakefield gives a chilling, commanding performance as a character who has no name but to whom he assigns one anyway: Pure Evil.

As co-writer of the Assault on Precinct 13 remake and The Negotiator, DeMonaco knows how to wring suspense from a simple scenario — letting the Sandins defend their home with smart, barbarous efficiency. Better still, he trusts Hawke — who’s almost better in these B-movie beasts anymore than anything prestigious without Before in its title — to deftly explore the grindhouse-gray morality when he weighs Bloody Stranger’s life against the lives of his family.

Ultimately, the siege sequence is undone by one too many sneak-up-and-shoot-’em moments, a poor sense of the size or floor plan of the Sandins’ home, some dopey decisions from daughter Zoey, and the overused trope of killers in creepy masks (howdy, Strangers!).

But let’s go back to that initial setup, easily the movie’s smartest, most interesting asset.

Set just nine years from now, the film plausibly implies the Purge could’ve been part of a 2016 presidential candidate’s platform. (It is, after all, discussed in Charlie’s history class.) Our divisive rhetoric and intolerable strife have given way to this decisive action. Not for nothing is the adjectivally loaded choice of a TV newscast to describe it as an outlet for “American rage.”

The Purge feels like the fictitious offspring of America’s shotgun marriage between real-life, tenuous policies and discordant political bluster. It’s also clearly a terrible idea. At no point does DeMonaco suggest anything to the contrary. But from a political point of view, he merely invites you to the wedding and lets you decide on whose side you’d like to sit. And in this ceremony, there’s definitely not a sermon.

While the film takes a definitive stance on how it feels about the Purge, it’s remarkably, refreshingly, devoid of a specifically partisan agenda. If that sounds like a copout, know that the Purge feels like a worst-case compromise among religious extremists, Tea Partiers, ultra-liberals, flip-floppers and everyone else on the Hill.

“I will become a better person, and you will have made a great sacrifice,” shouts one of the well-dressed blue bloods prepping to purge. Tell me that line doesn’t simultaneously aim at right-wingers who cover their cowardice in religion’s cloak and left-wingers who think only in terms of what to give up for a greater good. (Also, Hodge’s military man never speechifies about how the country he fought for has let him down; only because of dog tags dangling from his neck do we know he’s a vet.)

Even more interesting, and incendiary, are the film’s religious trappings and iconography. The Sandins, among others on their affluent street, set out a pot of blue flowers as a show of support for the Purge. Just as the Jews painted lamb’s blood on doors during Passover to assure their salvation, so, too, do these citizens to promote safety from passing angels of death.

And many of those who purge speak of it with the fire-and-brimstone fervor of Old Testament talk — almost like a rite to be invoked, inspired by the idyllic future they think it will help secure. (As Charlie’s characterization is to the Don’t Go In There Rule, so is this to a perfect workaround on the Fallacy of the Talking Killer, through which people soliloquize first and shoot later.)

What The Purge can’t circumvent is a finale that spins out into almost unintentionally amusing territory, thanks to a twist that DeMonaco rather terribly telegraphs in the first act. Even then, it finds a way to elevate its meaty discourse to a new level. Saying how, exactly, would be a spoiler, but like The Purge itself, what looks dumb on the surface has smarts to spare.