When the government spends money on the military, the investment payback to society is low. For example, if the government decides to build a un-needed bridge, at a minimum the local population does leverage the bridge to build up their economy. Even such an expensive project, if done when not economically warranted, pays back to society.
If a battalion is stationed in a foreign country, the military spends in that local economy. A missile, after built, when used, does not give back a return on investment. The items built, and labor spent, does not produce a product that American Society can leverage.
Granted, the world is not one we can merely trust and disband the military. America, as any leading nation, must have a military that can defend itself. And if needed wage war to protect it's interests.
So while I do support the concept of America having an army, I don't believe it should be spending 5% of total GDP on the military. Think of it this way, if every economic transaction had a 5% "surcharge" tax to pay for war, to avoid deficit spending, would the support for the large military system exist? Or would a 1% surcharge be more supportable?
Click to read topic by Mish, and an eye-catching graph to highlight America's over-allocation to military spending.