Cutting defense by 50% would crash the economies in several US cities who rely on the aerospace biz, damage a lot more that make their money supporting major military installations logistically, as well as basically grounding Air Combat Command and pretty much all non-transport air operations worldwide, mothballing 2/3 of the carrier groups and most of the subs, and throwing about half a million military personnel and another half a million civil service employees onto the unemployment rolls (Which would crush that system).
It'd pretty much stick a fork in the economy when you get down to it. On the plus side, I guess it would make gas cheaper since the military wouldn't be using very much of it. Doesn't seem like a very good trade-off to me, but then I lack the hyper-sophisticated comprehensive knowledge of everything the DUmmies claim to have.