The question I have is, how much should the US be spending in a time when it's the only global superpower, and its security interests are primarily threatened by small, isolated regimes and guerrilla/terrorist groups? Because we're sure as hell spending a lot now.
We're spending over $200 billion more a year *now* than we were when we "bankrupted" the Soviets with a massive arms race. (OK, fine, I'll use a real source)
Historically, though, we're not spending radically. We spend 4.8% of our GDP on defense. Despite the staggering numbers, this is actually an historic . "[N]ational defense spending was below 5 percent only in the late 1940s, late 1970s and since the start of the early 1990s." So, after the end of WWII, and then after Vietnam, and then after the Reagan administration. According to the World Bank numbers cited above, we didn't even hit 5% during the height of the Iraq and Afghanistan conflicts.
I'm not saying that defense spending doesn't need cuts, or that those cuts would destroy our national safety. I also think that the idea that defense spending will destroy the US is silly. It's clear that entitlement spending is the real threat. We also likely need tax increases, but entitlement spending has to be the first thing everyone thinks of when they think of cutting spending. There is simply no way to dig ourselves out of this hole, even if we cut every Army division and sold our aircraft carriers to bored billionaires to convert into pleasure craft.