Delusional, self-destructive liberals control political debate and simply will not allow any kind of collective punishment to occur. So "moderate" Arab muslims simply have no incentive at all to turn in their murderous brothers.
You are right, I doubt we have the national will to do what is necessary to defeat this enemy. The Left has so emasculated the American body politic that I doubt we will ever again (well, at least in my lifetime: I am in my 50s) develop the brass danglers that we will need to win this war on our culture and our civilization. The Left in America actually hopes we will lose such a conflict.