Our country's entire concept of crime prevention doesn't work on terrorists. We try to prevent crime by punishing criminals, trying to scare would-be criminals with the death penalty and such - look, if you do wrong, think of the consequences. These techniques are very poor against criminals in general (this has been statistically proven; harsher penalties do not reduce crime rates), but especially poor against someone as desperate and determined as a terrorist. Our other major technique is trying to capture them before the fact. This is marred by constant mistakes because it's very hard to exactly identify terrorists. The result is that we end up disturbing the lives of the people and killing many innocents, which of course just increases resentment towards us and breeds more terrorists.