So let's spray the Afghan poppy fields with weed killer. Repeat as often as needed.
I think many of our troops on the Stan wish it was so simple. The Americans, to some degree, want to do just that, while the Brits (quite probably correctly) see such moves as a guarantee of turning a 90% of the time peaceful farmer into a 100% of his time Taliban.
As I read that resignation letter, before I got to the writer's reference to Vietnam, I was thinking how incrediblly closely the situation with the US and the current (US/UN-appointed) Afghan Government parallels the situation in the early to mid sixties during the time of Diem and the series of generals who followed him pre-Thieu.
As history is wont to repeat itself, one can only wonder if the current Afghan President, (when, like Diem, he is deemed by Washington to be not delivering the goods), might meet a similar fate to Diem's. Nothing would surprise me. What might keep him alive is the sad fact that there's probably no one in the wings who the Americans consider suitable to fill the void.