Now we get to the heart of the matter, which is why are there terrorists in the first place?
My opinion is that, in the case of Islam, terrorists exist because they cannot achieve their goals through conventional means. In order to end terrorism therefore, we have to either (a) allow terrorists to have their goals or (b) destroy the terrorists.
What are the goals of the terrorists? The two main ones, stated time and time again, are to achieve a new world order in which fundamentalism Islam is the supreme religion, and in the process eradicate Israel and weaken the west. Since I find these to be unacceptable goals, I believe our only option is to destroy the terrorists. And again, I don't see how we can accomplish this without killing some of them, or a whole lot of them.