If the U.S. doesn't lead in the world, then sooner or later, by sheer force of numbers, we will be forced to follow, and that is a threat to our way of life. Believe you me, if we weren't so strong and influential in the world, entities like the UN would be walking all over us, just like they walk all over the puny and weak countries. The U.S. doesn't exist alone in the world, we have to work in the world, and as long as we're the sole superpower, we can exert our influence on the world, rather than the other way around.
And it is people like me, like President Bush, pragmatic optimists, who wrote the U.S. Constitution, not cynical, pessimistic scaredy cats, afraid of things going bump in the night, like you.