Thanks to friend Dirk van Nouhuys for the link, and to the Washington Post for making it available in the first place. Here follows a carefully considered argument from much deeper knowledge of Afghanistan for what I was arguing, much more cursorily, in my note yesterday.
According to this former US Foreign Service officer, the US is merely a bit player in "a 35-year old civil war" between "urban, secular, educated and modern Afghanistan against the rural, religious, illiterate and traditional," the latter being the main backing of "the Pashtun insurgency." The US military presence, backing a notoriously corrupt and non-Pashtun government and sending Afghan troops of other ethnicities to attack in Pashtun territory, simpy gives that insurgency greater legitimacy as Pashtun tribesmen see it. Here is the pdf. of Hoh's letter: John Hoh's letter of resignation (10 September 2009)