Leading article: Mexico's stark reminder of the cost of prohibition

Even by the barbaric standards of Mexico's drug criminality, the discovery this week in the north-east of the country of a mass grave with 72 bodies – including 14 women – is shocking. It is also a reminder of the root cause of the violence that has killed an estimated 28,000 people since president Felipe Calderón declared domestic war on the drug cartels almost four years ago. The mayhem reflects above all one simple fact: that the United States, which shares Mexico's 2,000-mile long northern border, is the world's largest consumer of illegal drugs.

The size of this clandestine market obviously cannot be calculated with precision. But the best guesses put it at $60bn or more per year and suggest that 70 per cent of the flow of illegal drugs into the US is controlled by Mexican cartels, which have long since supplanted their Colombian counterparts as the driving force in the region's drug business. Cocaine, heroin, cannabis or methamphetamine – whatever the US user's substance of preference, the overwhelming likelihood is that it will have transited though Mexico.

The cartels, by the admission of the federal authorities in Washington, now have operations in 200 US cities, double the total of just three years ago. They are now classified by the FBI as the biggest organised crime threat facing the country. And not only do the Mexican cartels fuel American consumption; the US also fuels the violence south of the border. While drugs flow north, not only money – probably tens of billions of dollars annually, both in cash and via ever more sophisticated money laundering schemes – flows south, but also the weapons with which the drugs wars are largely fought. Firearms cannot legally be sold in Mexico. The situation in the US, as is well known, is somewhat different.

This colossal traffic continues despite much tighter US surveillance of its southern border, in part to stem illegal immigration, and despite Mr Calderón's use of the army to try and eradicate the cartels. Regional co-operation has also never been stronger, exemplified by the 2007 Merida Initiative, involving Mexico, the US and other Central American countries, providing upwards of $400m a year for training, equipment and intelligence-gathering to take on the drug lords.

Some argue that the surge in violence – which has turned some border towns like Ciudad Juárez across from El Paso in Texas, into war zones – is proof that the pressure is working, turning the cartels against each other. But for every step forward there is a step back. Corruption remains a massive problem. The President was obliged to send in the troops because the poorly paid Mexican police had been infiltrated by the cartels; even so, reports suggest that in some areas the latter's power is, if anything, growing. By this reading, the violence suggests merely that turf wars are becoming more vicious, for a larger slice of an ever more lucrative market. In short, Mexico and the US are losing the drug war.

So what is to be done? Obviously there can be no let-up in efforts to break the grip of the cartels. They are not supported by the general population – indeed, take drug-related criminality out of the equation, and Mexico's murder rate is much lower than several other Central American countries. Yet so widespread and baneful is their influence that some experts warn of Mexico as a potential "failed state". That is an exaggeration, but excesses on one side provoke excesses on the other, and arguments for a new approach are multiplying.

Which brings us back to the root of the problem. If Americans lost their taste for drugs, the Mexican cartels would be out of business. That, however, will not happen; indeed the forbidden nature of drugs may make them more attractive. So why not legalise them? The argument has been powerfully made before and will be so again, but probably to no avail. Sadly the barbaric drug wars will continue.