Greg Scoblete ponders it:
On the one hand, continuing to bomb Afghanistan (and Pakistan) runs the risk of generating more ill-will and more recruits for the Taliban and/or al-Qaeda. In this sense, NATO strategy could easily be stuck in a terrible feedback loop (if it isn't already): we bomb insurgent targets (even those strictly affiliated with al-Qaeda), passions are aroused, new fighters join the fray, those fighters are bombed, and around and around we go.
On the other hand, how much can the U.S. really opt out of this feedback loop? Imagine a dramatically scaled back effort that sees the U.S. and NATO not only draw down most of its combat troops from Afghanistan but also limit its drone strikes to very "high value" and hard to reach targets. Presumably this would still enrage future Faisal Shahzads, would it not?