Seriously? So following your logic the US should just let al qaeda access to weapons and let them vent off in NY.

"would there be offensive actions by [al qaeda]: almost certainly. But they'd likely be on a scale many orders of magnitude smaller than [US's actions in Afghanistan] to date, and I doubt they'd be sustained"

I hope I'll never live in a country that will allow their citizens to die in order to appease some murderous religious group.