WASHINGTON—A decade ago, the U.N. General Assembly set an objective of “eliminating or significantly reducing” narcotics cultivation and trafficking “by the year 2008.” According to the data of the U.N. Office on Drugs and Crime, the effort has been an unmitigated disaster. Opium and cannabis production have doubled, while cocaine has slightly increased. The same proportion of adults—5 percent—consumes drugs today, mostly marijuana, as in 1998.

As officials from around the world gather in Vienna this week to chart the next decade of the anti-drug effort, it may be time to rethink the entire approach.

Echoing the Prohibition era in the United States, illegality has engendered organized crime empires that, in order to supply narcotics, undermine the peace and institutions of many countries. The latest example is Mexico, where President Felipe Calderon has unleashed the wrath of the state against the drug lords. The war between the state and the cartels, and among the mafias themselves, has mostly taken place in northern cities such as Ciudad Juarez, Tijuana, and Culiacan. Ten thousand people have been killed and drug-related corruption has been exposed at the highest levels, including the attorney general’s office.

The anti-drug budget worldwide is staggering: the United States alone devotes more than $40 billion yearly to the effort. Yet whenever attempts to limit supply manage to raise street prices in one country, prices go down in other countries: in Europe, the price of cocaine has dropped by half since 1990. But the crackdown has reduced the purity of the drug, increasing the harm to people’s health. According to the police, in Britain the purity has decreased from 60 percent to 30 percent in a decade.

Not to mention the consequences to individual liberty. Those who banned alcohol in 1920 felt compelled to amend the Constitution before they could pass Prohibition. No such amendment was ever presented to legitimize what Richard Nixon first called the “war on drugs” in 1971. The excesses committed in its name have created all sorts of social stigmas—including the fact that about 30 percent of black males in America spend some time in jail in large part due to drug-related offenses.

Three Latin American former presidents—Brazil’s Fernando Henrique Cardoso, Mexico’s Ernesto Zedillo, and Colombia’s Cesar Gaviria—recently put out a report condemning the war on drugs as a counterproductive failure, advocating a public health-based approach instead of repression. In anticipation of the meeting in Vienna, the latest issue of The Economist magazine, the bible of many current and aspiring enforcers of the law, devoted its cover, a survey and an editorial to making the case for legalization. For years, conservative publications such as The Wall Street Journal have run articles expressing the same view, including those by its expert on Latin America, Mary O’Grady. Leaders on the right (Henry Kissinger) and organizations of the center-left (George Soros’ Open Society Institute) have also spoken out on the issue.

No one knows exactly how drug use would be impacted by its legalization or its decriminalization. In countries where it is severely punished, consumption is high, which might mean that it would stabilize or even drop. Many European countries—Spain, Portugal, Italy, several Swiss cantons—have extremely lenient drug policies; consumption in those countries (except for Spain) is not very high. But even assuming a moderate increase in consumption, decriminalization or legalization would eliminate or substantially diminish the horrific side effects of the current war.

A movement in favor of legalization has existed in the United States for years. Because it is associated with the cultural war that has raged since the 1960s, its impact has been small. But the debate goes on. In many states the police do not go after personal possession of marijuana, and California is considering a bill that would make it legal. The vestiges of Puritan dogmatism—which H.L. Mencken memorably called the “inferior man’s hatred of the man who is having a better time”—have made it difficult to open a serious debate nationwide.

Today we regard the Opium Wars of the 19th century—by which the British retaliated against China for clamping down on opium imports—as crazy. One and a half centuries from now, people will read in total amazement that so much blood and treasure was wasted in the failed pursuit of a private vice that a relatively small percentage of the world population was not ready to give up.