The constraint of other regional powers which have an interest in the Afghan territory requires much more than aiding a few destitute resistance fighters. Without sounding apocalyptic, chaos in the region without our heavy handed stabilization could result in a major world war.
There is no contradiction in the proposal outlined. Support of the resistance is necessary for the removal of Bin Laden. But, they are not sufficient for stabilization in the region. Your (a) is not possible without first (b).
Sorry, I don't buy it. The successful reversals of communism fit my model, not yours. Allende, not Diem.