When we talk about volunteer organizations, we mean the employees work for free. Volunteer firefighters, search and rescue volunteers, disaster recovery volunteers, and little league coaches are volunteers, and that means they donate their time.
People who work for the Defense Department and other military-related agencies are paid to do it. They are volunteers in the same sense that all paid employees of all organizations are volunteers: they aren't forced to work for the organization. It's nice that the people who are paid by the defense department aren't conscripted to do so, and that they won't get thrown in jail if they don't. And it's good that they get paid for their work.
It's hard to argue that much of the trillion dollar military budget is of general benefit to society. It certainly isn't necessary for defending the nation's borders; the nuclear subs, bombers, and missile silos do a good job of that, and they collectively account for a small fraction of the budget. And why would we need a separate "homeland" security department if the "defense" department was really there simply to defend US borders from an attack by another country?
But this is a debatable point. A lot of Americans, like Mitt Romney, like having a big military, and would even like it to be even bigger. That's OK. A lot of Americans like big things: TVs, SUVs, houses, breasts, etc. It's a free country, and people are entitled to their opinions.
But what we need is a truly all-volunteer military. All those who like a big military should volunteer to work for it. True, it can be a very dangerous profession, and one that can lead to serious long-term physical and psychological damage. This is an even stronger argument for having the folks that like their military to be big be the ones volunteering to work for it.
Failing that, at the very least, it should be paid for on a voluntary basis. This is very doable; all we need is a check-off at the end of the IRS form 1040, similar to the one where you can donate a dollar of your tax refund to the presidential election fund. But it might need to be a bit more than a dollar. Let's do the math:
Assuming that mostly conservatives like a big military, and that they make up about half the population, that accounts for about 60 million households. But it's a safe bet that most of them would prefer that someone else pay for it: that's exactly why they think it's about the only thing that should be funded with taxes. Assuming a tenth of them are actually willing to step up to the plate, that accounts for a large number--six million households--who can cover the tab for the military. So, dividing this into the trillion dollar cost of the US military, the amount next to the check-off box would need to be only:
Ö $167,000
