It's the never-ending war on drugs, of course. Steve Chapman at Reason has a nice take:
By now, it should be clear that using force to wipe out the drug trade is a task on the order of bailing out the Atlantic Ocean with a teaspoon. Law enforcement can interdict shipments and imprison dealers, but the success is invariably short-lived. Each seized cargo is an opportunity for another seller to fill the gap. Each arrested trafficker is an invitation for a competitor to grab his business. The more vigorous and successful the law enforcement campaign, the higher the prices drug suppliers can command"”and the more people will be enticed to enter the market. It's a self-defeating process. All this would be academic if Americans (and Mexicans) would simply lose their taste for illicit drugs. But we might as well hope the Sahara Desert will run out of sand. There has always been a demand for mind-altering substances, and there always will be. That's why, despite all the resources the U.S. government has expended on locking up sellers and their customers, drug use is higher today than it was two decades ago.