Does free college threaten our all-volunteer military? That is what Benjamin Luxenberg, on the military blog War on the Rocks says. But the real question goes beyond Luxenberg's practical query, striking deep into who we are and what we will be as a nation.

Parade participants protesting against high student loan burdens are preparing to take part in the annual July 4th parade at Ashland, Oregon, U.S. on July 4, 2015. REUTERS/Randall Mikkelsen

Unlike nearly every other developed country, which offer free or low cost higher education (Germany, Sweden and others are completely free; Korea's flagship Seoul National University runs about $12,000 a year, around the same as Oxford), in America you need money to go to college. Harvard charges $63,000 a year for tuition, room, board and fees, a quarter of a million dollars for a degree. Even a good state school will charge $22,000 for in-state tuition, room and board.

Right now there are only a handful of paths to higher education in America: have well-to-do parents; be low-income and smart to qualify for financial aid, take on crippling debt, or...

Join the military.

The Post-9/11 GI Bill provides up to $20,000 per year for tuition, along with an adjustable living stipend. At Harvard that stipend is $2,800 a month. Universities participating in the Yellow Ribbon Program make additional funds available without affecting the GI Bill entitlement. There are also the military academies, such as West Point, and the Reserve Officers’ Training Corps, commonly known as ROTC, which provide full or near-full college scholarships to future military officers.

Overall, 75 percent of those who enlisted or who sought an officer’s commission said they did so to obtain educational benefits. And in that vein, Luxenberg raises the question of whether the lower cost college education presidential nominee Hillary Clinton proposes is a threat to America's all-volunteer military. If college was cheaper, would they still enlist?

It is a practical question worth asking, but raises more serious issues in its trail. Do tuition costs need to stay high to help keep the ranks filled? Does unequal access to college help sustain our national defense?

Of course motivation to join the service is often multi-dimensional. But let's look a little deeper, and ask what it says about our nation when we guarantee affordable higher education to only a slim segment of our population. About seven percent of all living Americans were in the military at some point. Less than 0.5 percent of the American population currently serves. Why do we leave the other 99.95 percent to whatever they can or can't scrape together on their own?

The issue of how to pay for broader access to higher education always comes up, and was used by Hillary Clinton to knock down some of Democratic primary rival Bernie Sanders’ more aggressive proposals. Republican White House candidate Donald Trump may bring up the same question in the upcoming debates about Clinton’s more modest plans.

Money does matter, but what the country can get for its money is also important. We’ll leave aside the not-insignificant question of how so many other developed nations manage to pay for their citizen’s education, and stay in America.

As a kind of thought experiment, let's begin by rounding off the military higher education benefit, tuition and living stipend, to $53,000 a year. We’ll note a single F-35 fighter plane costs $178 million.

Dropping just one plane from inventory generates 3,358 years of college money. We could pass on buying a handful of the planes, and a lot of people who now find college out of reach could go to school.

The final question many people will be asking at this point is one of entitlement. What did those civilians do that the United States should give them college money?

Ignoring the good idea of expanding “service” to include critical non-military national needs, the answer is nothing. If we started giving out the funds today, those civilians did nothing for them. But maybe it is more important than that.

Security is defined by much more than a large standing military (and that does not even touch the question of how, say, an eight year occupation of Iraq made America more secure). The United States, still struggling to transition from a soot and steel industrial base that collapsed in the 1970s to something that can compete in the 21st century, can only do so through education. More smart people equals more people who can take on the smarter jobs that drive prosperity. It is an investment in one of the most critical forms of infrastructure out there – brains.

To be sure, the issue of how much the United States should spend on defense, and how that money should be allotted, is complex. But the changes to spending discussed here exist far to the margins of that debate: the defense budget is some $607 billion, already the world’s largest by far. The cost of providing broader access to higher education would be a tiny fraction of that amount, far below any threshold where a danger to America’s defense could be reasonably argued.

No one suggests veterans should have their benefits reduced. But for a nation that can clearly afford to pay for a broader base of accessible higher education if it wants to, it seems very wrong to simply leave the nation’s future to a Darwinian system of financial survival.