A proposed directive by General John Craddock, Nato’s top commander, to target opium traffickers and “facilitators” in Afghanistan has provoked considerable opposition within the alliance. That resistance is warranted, since Craddock’s proposal is a spectacularly bad idea. Implementing this proposal would greatly complicate Nato’s mission in Afghanistan by driving Afghans into the arms of the Taliban and al-Qaida.

US and Nato leaders need to understand that they can wage the war against radical Islamic terrorists in Afghanistan or wage a war on narcotics — but they can’t do both with any prospect of success. The opium trade is a huge part — better than one-third — of the country’s economy. Attempts to suppress it will provoke fierce opposition. Worse yet, opium grows best in the southern provinces populated by Pashtuns, a people traditionally hostile to a strong central government and any foreign troop presence. These same provinces produced the Taliban and more easily revert to supporting fundamentalist militias than their Tajik, Uzbek and Hazara neighbours to the north.

Alternatives to opium offer little hope. More than 90% of the world’s opium comes from Afghanistan. Taking on opium in Afghanistan means taking on the world’s demand for opium. Opium purchases for medicinal uses and substitute crop programmes with wheat, saffron and pomegranates will not stanch the demand for illicit drug production. In fact, reducing the illegal harvest with these efforts only makes the black-market prices rise and encourages farmers to grow more. If the Cold War taught us anything, it is that you cannot fight economics.

Proponents of a crackdown argue that a vigorous eradication effort is needed to dry up the funds flowing to the Taliban and al-Qaida. Those groups do benefit from the drug trade, but they are hardly the only ones. A UN report estimates that more than 500,000 Afghan families are involved in drug commerce. Given the network of extended families and clans in Afghanistan, it is likely that at least 35% of the country’s population has a stake in the drug trade. Furthermore, Nato forces rely on opium-poppy farmers to provide information on the movement of enemy forces. Escalating the counter-narcotics effort risks alienating these crucial intelligence sources.

Equally important, many of President Hamid Karzai’s key political allies also profit from trafficking. These allies include regional warlords who backed the Taliban when that faction was in power, switching sides only when it was clear that the US-led military offensive in late 2001 was going to succeed. Targeting such traffickers is virtually guaranteed to cause them to switch sides yet again.

Targeting drug traffickers also makes it impossible to achieve any “awakening” on par with the American success in Sunni areas of Iraq. We cannot fund local militias to keep the Taliban out. These militias already pay themselves from drug profits. These same drug profits will keep them loyal to Nato’s enemies as long as the alliance remains committed to destroying their livelihood.

Nato leaders need to keep their priorities straight. The principal objective is to defeat radical Islamic terrorists. The drug war is a dangerous distraction from that goal.

Recognising that security interests sometimes trump other objectives would hardly be unprecedented. For example, US officials eased their pressure on Peru’s government regarding the drug-eradication issue in the early 1990s, when Lima concluded it was more important to induce farmers involved in the cocaine trade to abandon their alliance with the Maoist Shining Path guerrillas.

The Obama administration should adopt a similarly pragmatic policy in Afghanistan and look the other way regarding drug trafficking. Alienating crucial Afghan factions in a vain attempt to disrupt the flow of drug revenues to the Taliban and al-Qaida is a strategy that is far too dangerous. This war is too important to sacrifice on the altar of drug-war orthodoxy.