One of the very few good things the Taliban did while in charge of Afghanistan was crack down on opium farming as an immoral activity. However, one has to contrast that against the many bad things they did, such as executions on flimsy premises, destruction of ancient cultural artifacts, and providing a base of operations for Al Qaida, from which they launched the African embassy attacks, the USS Cole attack, and the 9/11 attacks.
One of the unfortunate side effects of deposing the Taliban was the resumption of opium farming. The coalition forces that are in Afghanistan right now have their hands full trying to deal with a resurgent Taliban presence. The current Afghan government is either incapable of, or possibly unwilling to, interrupt opium farming.
Afghanistan is a poor country. Any income is a very dear thing to the residents. Opium happens to be a fairly lucrative cash crop. To them, it's not selling poison, it's feeding their families. Doesn't work out that way when the product reaches the final consumer, but the addicts are continents away, while the farmer's family is right in front of them. Which brings up another unpleasant choice... crack down on opium farming while not offering any alternative, and the tribes turn against you. Afghanistan in decades past, and Vietnam, show what happens when the endemic population of a country turns against an occupying force.
So, rather than conspiracy theories about the US promoting opium growth, what we really have is a no win choice. Leave the Taliban in place and get more terrorist attacks. Knock them out, and as a side effect, opium production resumes, and probably will remain in production until Afghanistan has a stable government willing to choke off the opium farming by offering a viable income alternative.
Unfortunately, Afghanistan hasn't really had a stable government in all of history... it has always been, and probably always will be, a collection of regional tribes.