What I would now say (having been corrected) is that whether they kill a lot of people or not, they are then police problems, not military problems. No war needs to be launched to stop such attacks and no war can do anything about them.
I can understand the logic behind this statement, but I am not entirely convinced this is true. I definitely agree there is no requirement for large military forces to occupy foreign lands to fight terrorism, but I think there is still a major (I would argue a critical) role for intelligence and special operations forces to continue waging a war against these groups in the shadows. That is sustainable long term (from the cost perspective) and I think ultimately more effective. The example given for this thread was a homegrown threat that clearly was a police problem, but his mentor Anwar Awlaki was an intelligence/SOF problem, as are many others who plan and inspire operations against the U.S. from afar. The police can only act defensively, which doesn't give us much depth when it comes to defense. I think an offensive element for this conflict is critical.