Bill Maher has an excellent clip on this. He boils it down to, "Basically we're arming Al Qaeda."

http://www.youtube.com/watch?v=M6paYu3GM2Y

Bin Laden's overall strategy against much larger enemies such as the Soviet Union and United States was to lure them into a long war of attrition in Muslim countries, attracting large numbers of jihadists who would never surrender. He believed this would lead to economic collapse of the enemy nations. Al-Qaeda manuals clearly express this strategy. In a 2004 tape broadcast by al-Jazeera, bin Laden spoke of "bleeding America to the point of bankruptcy". [1]

[1]http://en.wikipedia.org/wiki/Osama_bin_Laden#Beliefs_and_ide...