As long as islamist and totalitarian regimes exist you have no choice but to continue it if you want to maintain your current lifestyle. There are actors in this world whose stated goal is the eradication of American prosperity. The only effective way to deal with them is through the war machine. It's unfortunate but such is the current state of the world. Libertarian ideals can only be realized in an environment in which participants share basic common values. The ayatollahs don't fall under that category.