Why are we in Afghanistan?

By overthrowing the Taliban, we've just taken out a government that restricted the opium trade; what happened to the war against drugs? Furthermore, the Afghan citizens want the US gone. The Taliban is not nearly rich enough to acquire weapons of m destruction, especially if they don't condone the drug trade. We haven't found Osama Bin Laden, and even if we needed to, was the use of that many troops necessary? We have drones in Pakistan; we could have done the same thing in Afghan and even lulled him into a false state of security. But whatever, the past is done; I won't argue with the effectiveness of the war against terrorism, as muslim support for fundamentalism has dropped heavily. The question is why we're still in here if the people want us gone and the Taliban pose no significant threat?