Incidentally, no one is saying the Pentagon should be immune to budget reductions. But wholesale cuts--made with little regard for national security--will do more harm than good, and inevitably cost even more. Lest we forget, one reason that Ronald Reagan had to spend so much on the military is because predecessors, Gerald Ford and (especially) Jimmy Carter, created the "hollow force" of the 1970s.
Thankfully, that era was over by the time I signed up, but I heard plenty of horror stories from those who served in the post-Viet Nam military. In some instances, crews had to cannibalize multiple aircraft just to get one jet in the air. Multiply those logistical problems (and training issues) across DoD, and you've got some idea of the Carter-era military.
While we can't afford massive increases in defense spending (at least right now), we can't afford a return to the hollow force, either. Balancing resources against security priorities will be a major challenge in the years ahead. Unfortunately, neither the Obama Administration--or Congress--has articulated any sort of strategy that could drive this process.