(Bernd DebusmannBernd Debusmann is a Reuters columnist. The opinions expressed are his own)

Tough marijuana laws are driving millions of Americans to a more dangerous mood-altering substance, alcohol. The unintended consequence: violence and thousands of unnecessary deaths. It’s time, therefore, for a serious public debate of the case for marijuana versus alcohol.

That’s the message groups advocating the legalization of marijuana are beginning to press, against a background of shifting attitudes which have already prompted 13 states to relax draconian laws dating back to the 1930s, when the government ended alcohol prohibition and began a determined but futile effort to stamp out marijuana.

How dismally that effort has failed is not in doubt. Marijuana is so easily available that around 100 million Americans have tried it at least once and some 15 million use it regularly, according to government estimates. The U.S. marijuana industry, in terms of annual retail sales, has been estimated to be almost as big as the alcohol industry — $113 billion and $130 billion respectively. On a global scale, marijuana is the world’s most widely used illicit drug.

Since the United States, and much of the rest of the world, plunged into a recession last year, the most frequently used argument in favour of legalizing marijuana has been economic: if it were taxed, the revenue would help stimulate economic recovery just as a gusher of dollars in fresh tax revenue from alcohol helped the United States pull out of the Great Depression after the 1933 repeal of prohibition.

That idea enrages some leading drug warriors, including the head of the United Nations Office on Drugs and Crime, Antonio Maria Costa. In the preface to the U.N.’s 2009 World Drug Report, he asks whether proponents of legalization and taxation also favour legalizing and taxing human trafficking and modern-day slavery “to rescue failed banks.”