In April, the world’s governments will meet in New York for a special assembly at the United Nations to discuss how to solve the drug problem. Don’t hold your breath: Since the previous such gathering nearly two decades ago, the narcotics industry has done better than ever. The number of people using cannabis and cocaine has risen by half since 1998, while the number taking heroin and other opiates has tripled. Illegal drugs are now a $300 billion world-wide business, and the diplomats of the U.N. aren’t any closer to finding a way to stamp them out.

This...