I find it very difficult to work out whether we (Britain and America, the West) should be in Afghanistan; anyone who thinks it easy to answer hasn't thought about it enough. But Marc Lynch at Foreign Policy (who also has an open mind) poses a good question:
Suppose the U.S. succeeded beyond all its wildest expectations, and turned Afghanistan into Nirvana on Earth, an orderly, high GDP nirvana with universal health care and a robust wireless network (and even suppose that it did this without the expense depriving Americans of the same things). So what? Al-Qaeda (or what we call al-Qaeda) could easily migrate to Somalia, to Yemen, deeper into Pakistan, into the Caucasas, into Africa --- into a near infinite potential pool of ungoverned or semi-governed spaces with potentially supportive environments. Are we to commit the United States to bringing effective governance and free wireless to the entire world?