Afghanistan's cultural, ethnic and tribal divides mean that it will never have a fully functional, accepted central government. They'd have to unite and defeat all the separate tribal forces and thats proved quite difficult, almost ridiculously so, in the past. Even if you DO beat them you have to comprehend the fact the most Afghans have tribal and not national loyalities. The PDPA tried and failed and they had waaaay more manpower.
How much are Americans willing to sacrifice for something not even certain to result in a victory? How much are the British and allied forces? We do not have the will to continue this war for as long as is necessary nor do we have the manpower or funding.
The goal is to defend the US from the ****ers, not to defend Afghanistan from its own people.
By securing Afghanistan from terrorism, you defend your nation from Afghanistan's terrorists.
"The darkest places in hell are reserved for those who maintain their neutrality in times of moral crisis."