bsharporflat:

Invading Afghanistan had little direct impact on the ability of Al Qaeda to conduct 9/11. You tell yourself this as an a priori fact but it just isn't true.

Did the 9/11 guys need Afghanistan to learn how to fly planes? Or perhaps only in Afghanistan do they have advanced level training in using box cutters? 9/11 training happened mostly in the USA. The contribution of Afghanistan training and indoctrination could have occurred anywhere in the world

You seem to assume a lot about what I think about Afghanistan. Regardless of my views on Afghanistan, I'm challenging you to justify your own weak reasoning.

First of all, the goal of invading Afghanistan was not to impact Al Qaeda's ability to conduct 9/11, since the invasion occurred after 9/11. The goal was to prevent other large-scale attacks, which may or may not have had anything to do with planes and box cutters. Second of all, I'm not sure that I understand your point that the training could have been conducted anywhere, so why invade Afghanistan. Didn't you previously argue that taking out terrorist camps in Afghanistan would have some worthwhile effect?

You seem to neglect the fact that the attacks were orchestrated from Afghanistan and that taking out the low-level operational cells is not sufficient to destroy a large terrorist group's operational capability because you can always recruit new low-level terrorists. To break the operational capability of a large terrorist group you need to attack the elements of the group that are not easily replaceable -- not only the ideological leadership, but perhaps more importantly the mid-level commanders who have experience and expertise in conducting large-scale operations abroad without being detected, managing finances, recruitment and training, etc. As of 9/11 most of those guys were in Afghanistan.

I notice that you keep on shifting your reasoning and ignoring relevant questions just as long as the end result is that invading Afghanistan is a folly. Perhaps it was, particularly in terms of the subsequent nation-building efforts, but the burdern is still on you to suggest a practical alternative that would have broken al Qaeda's operational capability (unless you are arguing that the best option for the United States would have been to absorb more attacks). Now, that alternative doesn't necessarily have to be military (perhaps you can think of a good way to deter or appease Al Qaeda), but it should be based on something more than hand-waving, fantasy, and ill-conceived rhetoric.