Like Prohibition before it, the “war on drugs” is a disastrous and costly failure that has needlessly imprisoned thousands of non-violent offenders, ruined countless lives, and made dangerous criminals richer — all without doing much to actually reduce the availability of drugs. That’s the message, more or less, of “Snitch.” And I agree with it. But I still don’t like “Snitch,” which is a pseudo-serious hand-wringing action drama that uses social importance to disguise its unoriginality.

The uncommonly tall, handsome, and muscular Dwayne Johnson plays an average, ordinary, everyday Midwestern father named John Matthews whose 18-year-old son, Jason (Rafi Gavron), gets set up in a DEA sting for which the federally mandated minimum sentence is 10 years. The law was meant to provide harsh penalties for big-time drug traffickers, but it’s mostly used against small-time non-pros like Jason (who foolishly agreed to accept a package of Ecstasy for a friend). The only way the sentence can be reduced is if the offender helps the DEA catch other drug dealers. But Jason, who is not a drug dealer or a drug user, doesn’t know any, and he’s not willing to entrap anyone the way he was entrapped.

His dad goes to the federal prosecutor, a humorless ball-buster named Keeghan (Susan Sarandon), and asks: What if I help you nab somebody? Would that count? It would, Keeghan says. As luck would have it, John Matthews owns a successful construction company, some of whose low-level employees have, shall we say, connections to the drug trade. One such fellow, reformed ex-con Daniel James (Jon Bernthal), agrees to put John in touch with a deadly thug named Malik (Michael T. Williams), unaware that John is working for the feds and thus risking both their lives.

If this were a standard “I’ll do whatever it takes to save my son” thriller, without the heavy-handed messaging, two major things would be different. For one, it would probably be a lot more fun to watch. As it is, the stakes are so high, the injustice so appalling, that we’re never really allowed to enjoy The Rock’s feats of derring-do. How can you find excitement in shootouts and high-speed car chases when poor Jason is being beaten up in jail every day? (John visits him frequently, lest we forget how tormented everybody is.)

The other thing that would be different if “Snitch” weren’t so agenda-oriented is that I wouldn’t mind its rampant use of familiar action movie cliches. Such tropes are fun when used in the service of a story not meant to be taken very seriously anyway. Regular joe John Matthews turns out to be an expert driver and a decent marksman when put in harm’s way; he outsmarts both the drug cartels and his DEA handler (Barry Pepper); he single-handedly achieves victory against the odds; yada yada. That’s all well and good in a throwaway action flick. But in a movie that’s “inspired by true events” and that claims to be about Important Things, it’s disappointingly implausible. “Snitch” is an action movie without the fun, and a social drama without the depth.

C (1 hr., 52 min.; PG-13, moderate profanity and violence.)