It’s easy to see why someone would want to make a movie about Ricky Wershe Jr. His life story, the inspiration for the new, fact-based crime drama “White Boy Rick,” has it all: drugs, sex and gunrunning, plus a main character whose neck-deep involvement in all those activities — while still a teenager — is both shocking and appealingly guileless.

It’s a little bit harder to explain why you should watch such a depressing, and at times even soul-sucking, movie.

Set in 1980s Detroit, at the height of the city’s crack epidemic and taking place in seedy East Side neighborhoods where kids hang out at the roller rink when they’re not shooting rats for fun (at least as depicted on film), “White Boy Rick” is permeated by an atmosphere of grimy hopelessness that makes it hard to watch.

Moments of dark humor and colorful dialogue leaven the bleak mood, as when Ricky’s father (played by Matthew McConaughey in a greasy mullet) describes this Wild West vision of late 20th-century urban America: It’s the only place, he says, “where a man can hot-wire his brains to his balls to make s--- happen.”

For Ricky’s old man, that translates to selling modified AK-47s, with the help of his son, to drug dealers and other shady customers — some of whom go on to commit horrible crimes. (In a drive-by shooting, a 13-year-old is killed in the crossfire.) The threat of prosecution by the FBI is used as leverage to lure Ricky (played by baby-faced Baltimore newcomer Richie Merritt) to go undercover as a 14-year-old drug informant. This is where the film starts to get interesting — if also, let’s face it, something of a downer.

Taking its title from the nickname bestowed on the younger Wershe by some members of Detroit’s black underworld, “White Boy Rick” covers a span of only three to four years. Yet within that brief window, the film charts its adolescent antihero’s unlikely rise and predictable fall, from law-enforcement operative to outlaw, when agents (played by a maternal Jennifer Jason Leigh and a businesslike Rory Cochrane) cut Ricky loose from the informant program. After that, he uses the skills he learned as a fake drug dealer to become a real one.

At one point, Ricky is shot in the gut in retaliation by a rival, leading to him wear a colostomy bag. French director Yann Demange (“ ’71”) doesn’t flinch about showing any of this, a frankness that the filmmaker turns into a kind of perverse stylistic asset when it comes to drawing our attention to the story’s most sordid details. Some of that unpleasantness concern Ricky’s older sister, Dawn, a drug addict played by an almost unrecognizable Bel Powley (“The Diary of a Teenage Girl”). Scenes of Dawn going through withdrawal after her father and brother rescue her from a crack den are harrowing, if also oddly touching, thanks to the familial affection.

At another point, Ricky — already baby-daddy to one girlfriend (Kyanna Simone Simpson) — gets seduced by the wife (Taylour Paige) of an incarcerated drug rival, a woman who also happens to be the niece of Detroit Mayor Coleman Young.

You can’t make this stuff up.

And screenwriters Andy Weiss, Logan Miller and Noah Miller don’t try, mostly hewing faithfully to the tragicomic contours of Ricky’s life. That trajectory leads to the film’s protagonist becoming, as portrayed here, a victim of politics. It’s a reading you may or may not choose to accept.

“White Boy Rick” is an engrossing-enough cautionary tale, if that’s what it is. It’s even an entertaining one, in an unsavory kind of way. But whether there’s any deeper meaning to a story that tries only halfheartedly to say something about the fragility of family is debatable. Still, the performances, which include cameos by Bruce Dern and Piper Laurie as Ricky’s grandparents, are all very good.

Is that good enough? I’m reminded of one exchange in the film, after Ricky’s dad has tried to convince his son that, despite all their tribulations, things have “worked out OK” for the Wershes.

“Dad,” Ricky reminds him, “your daughter is a junkie and I’m s----ing into a bag.”

“What can I say?” Ricky’s father replies. “I’m a glass-half-full guy.”

Warts and all, there’s enough to like about “White Boy Rick” that you may feel the same way.