The US military is indeed the most efficient of government endeavers because it has to be in order to survive, literally survive. Not so with all other government programs.
As for warefare being "the biggest, most destructive of all", duh, what was your first clue. War is an abomination. It is horrible. But, as long as evil people will resort to violence for evil purposes (and Islamic fascism is evil), then I very much want the US to have the badest, meanest military on the planet. I want to soundly defeat all who threaten us. Even better, I wish to deter all our foes from even thinking about attacking us.
If you think the US military is expensive and destructive, try to imagine loosing a war to radical Islam, or communist dictators.