Ludwig Von Mises once said that "Economically considered, war and revolution are always bad business." I agree. War is, by its very nature, the destruction of valuable and scarce resources (human and non-human). People's ways of living are always destroyed and, to give a 21st century example, agitate these same people into violence.
When we destroy, say, an opium poppy field in Afghanistan, we are also destroying someones way of life. These farmers must look elsewhere for work and other ways to provide for themselves, usually in areas of work that they are less skilled in (thus increasing their chances of earning lower wages). Many times these same farmers join militaristic groups to fight back against aggressive governments.
After destroying their only way of living, can we really blame them?
On a side note, who is to say that these farmers are using opium poppy seeds soley to fund a terrorist group, if at all? Who is to say these farmers can't sell these seeds to medical companies who want to produce pain reducing medications?
After all, opium poppy seeds do have medicinal purposes as well.
Also, just because we have a legalized culture of drug prohibition in the United States doesn't mean we can use military might to impose that culture on any foreign country.
In short, we choose the killing of livings by our intervention rather than helping farmers make a killing from their way of living by our non-intervention.
The other tragic aspect of war is that there are others who profit from war. It is for this reason that I am providing a link to the anti-war classic "War is a Racket" by retired U.S. Marine Major General Smedley Darlington Butler. The link in the previous sentence is to the online HTML version. However, if you want the PDF version click here.