Phil has a good point. It may not be politically smart to wipe out a whole bunch of (possibly conscripted) soldiers, when the psychological war may be just as effective.

From this source:

A Washington-based envoy for the northern alliance, which calls itself the United Front, said the defection of 1,200 Taliban troops and 40 officers prevented the Taliban from using a major road near Baghram Air Base near Kabul. The figures could not be independently confirmed. A U.S. official, speaking on condition of anonymity, said the claim has not been verified, but defections of Taliban forces have been expected.