Because if the world understood the full extent of our military power and what we can do with it, they would demand the same capabilities, and refuse to trade with us until they got it.
I do not believe that we see ourselves as "fighting for our very survival." We say the platitudes, but we really don't think that the Islamofacists will really change our way of life like Hitler would have.
If we ever come to the point where the populace believes that our survival is threatened, expect the bombs to rain over ANYWHERE and EVERYWHERE the terrorists may be hiding!