WASHINGTON — A new conventional wisdom is on the rise: Drug prohibition, or “the war on drugs,” is a costly flop. It not only failed to cut drug use and associated social ills significantly but has also imposed additional social costs far exceeding the benefits. Those costs include violent crime linked to the black-market drug trade as well as the mass arrest and incarceration of small-time users, a disproportionate number of whom are African American.

It follows that the only solution is legalization, at least of marijuana and maybe other substances. Apropos of Philip Seymour Hoffman’s death, for example, former congressman Barney Frank (a weekly columnist for the Maine Sunday Telegram) suggested legalizing heroin. Then we could abandon the fool’s errand of prohibition and concentrate on “harm reduction” strategies such as treatment.

There’s one problem: the tendency of legalization advocates to counter anti-drug hyperbole with hyperbole of their own. The data don’t actually show that drug prohibition is futile, that its negative side effects are worsening or that legalization would eliminate the social-policy dilemmas and trade-offs posed by drug abuse.

Does drug prohibition achieve its main goal, which is to discourage drug use and abuse? We can’t know what would have happened if drugs had been legal for the past few decades or, for that matter, if the United States had waged a war on drugs half as harshly as Singapore, where a 15-gram heroin stash can merit the death penalty.

But the data do make one thing clear: If the goal of the war on drugs is to limit demand for drugs, then you can’t say the authorities are losing. According to federally sponsored surveys that track drug usage, the rate of current-month powder and crack cocaine use dropped by half in the past 10 years. Meth use fell by a third; heroin use has remained flat.

True, marijuana use rose slightly overall – but it fell among 12- to 17-year-olds, a result that even legalizers should applaud since they generally don’t favor allowing minors to smoke.

Meanwhile, even as drug prohibition continued, violent crime and property crime fell, dramatically. Not only did the number of murders in the United States decrease from 24,703 in 1991 to 14,612 in 2011 but drug-related murders declined from 1,607 to 505, according to Justice Department statistics. Some 6.5 percent of murders were related to drugs in 1991, but only 3.4 percent were in 2011.

The drug arrest rate fell from 142.1 per 100,000 in 1991 to 97.8 per 100,000 in 2011. Yes, blacks were still 3.9 times more likely to be busted for drugs than whites in 2011 – but that ratio was down nearly 50 percent from the one recorded 20 years earlier.

Marijuana arrests account for a bigger share of drug arrests these days, 44.3 percent in 2011 versus 22.4 percent in 1991. But when you compare marijuana arrests to actual days of marijuana usage, the story’s different. By this measure, “enforcement intensity” fell 42 percent between 2007 and 2012, according to drug-policy expert Keith Humphreys of Stanford University.

Some “war.” It’s a myth that prisons are full of low-level pot smokers. Less than 1 percent of the state and federal prison population is doing time for pot possession alone; most of these prisoners are dealers who pleaded guilty to possession in return for a lesser sentence, according to the 2012 study “Marijuana Legalization: What Everyone Needs to Know,” published by Oxford University Press.

America’s worst new drug-abuse problem involves a legal substance, opioid painkillers, that’s supposedly available only by prescription.

I don’t mean to suggest that there are no good arguments for legalizing any currently illicit substance. The case for decriminalizing pot is strong, as long as accompanying limitations on use by minors and other regulations have real teeth.

But let’s discuss the issue on its actual merits – and not pretend that legalization is a panacea for drug abuse, and its related social ills, any more than prohibition was, or is.

— The Washington Post News Service with Bloomberg News