Why Afghanistan?

The New York Times ran a short piece detailing why nation building in Afghanistan is vital to counter-terrorism:

But most specialists on counterterrorism and counterinsurgency, inside and outside the government, say terrorism cannot be confronted from a comfortable distance, such as by airstrikes or proxy forces alone. It may take years to turn Afghanistan into a place that is hostile to Al Qaeda, they say, but it may be the only way to keep the United States safe in the long term. Many agree with the classified strategy for a troop buildup that Gen. Stanley A. McChrystal, the top commander in Afghanistan, has presented to Mr. Obama and the Joint Chiefs of Staff in recent days. [emphasis mine]

I'm struggling to understand why people believe this. First, Afghanistan is already hostile to al Qaeda - as al Qaeda is no longer in Afghanistan. Second, is Afghanistan the only place in the world where terrorists can congregate? Once we've taken Afghanistan off the chessboard, radical Islamic terrorists are defeated? Really? Does anyone seriously believe that?

(AP Photos)