Who cares? Kill them all. Let Allah sort them out!
It isn't that simple. The threat has gone global. Boka Haran is wreaking havoc in Africa. Libya is still destabilized because the US and NATO destroyed a perfectly wonderful dictatorship there. There are reports of those mad Chechnyans getting involved, and we saw with the Boston Marathon a year ago that Muslims from their neck of the woods have crazies in the US. Refugees are crossing the Med from Libya to Italy, plenty of them potential terrorists. France, England, and even some parts of China have Muslims ready to riot. This is serious stuff, caused by the US overthrowing govs that were dictatorships, for sure, but they pretty much kept their nutcases in line. These new nutcases on the block....ISIS....have learned the lesson. They fought the wars for the west, and don't see any point in giving the west power to in turn give them the Assad-Khadaffi-Sadam treatment.
I don't think anyone expected a terror group this powerful, savvy, and determined to arise from US-Saudi mis-steps in Syria.