Afghanistan is only a particular example of a general problem and Afghanistan is not the last time this kind of problem will come up.
Afghanistan was a problem before 9/11. Somalia continues to be a problem. The Rift Valley of Africa is an open sore for most of its length. Cambodia was one for decades.
As long as there are nation-states, there are going to be failed nation-states. With them comes a continuing real need for a formal international equivalent of a receiver-in-possession for failed nation-states. Having a flag and a UN seat and a top-level internet domain lets you be a nuisance to your neighbors and often a species of hell for your people.
Much of what I have read here about Afghanistan operates on the assumption that we're seeing, in Lenin's words, imperialism as the highest form of capitalism, and I don't think that describes the phenomenon at all.
In Afghanistan the West is ad-hoc-ing -- and not very well -- a solution to what is only one example of a species of problem that needs to have an institutional solution, one derived multilaterally, by the world community, for the sake of the peace of our shared planet and the safety of some of its poorest, most vulnerable inhabitants.
NATO and the US big-footing around may not be the answer to the problem, but that's not the same thing as saying there is no problem. And waiting for the inevitable withering away of the state isn't a very effective solution, either
This is something the nations of the world are going to have to grasp the nettle on sooner or later, with all its problems of sovereignty, 'interference in purely internal matters', etc.