The real problem is the crackdown on the opium trade which is putting the drug runners' money on the side of the Taleban. We should just buy the opium at the market price; or, preferably push the price higher than what the market will bear so as little opium as possible reaches outside Afghanistan-- it's cheaper than warfare, or paying the social and medical costs of cheap heroin in the developed world and spreads a lot of cash around Arghanistan.
Buy it and destroy it, for the reasons you mentioned. Seems like a win win all the way around to me.