Until a few years ago, I taught an undergraduate research and writing course at Cooper Union, in Manhattan’s East Village. Founded in 1859, Cooper Union is the namesake of Peter Cooper, who used his fortune from real estate, steel, railroads and glue to endow a college where education would be as “free as air and water” for aspiring architects, engineers and artists. The promise held up for more than a century.

But in the fall of 2011, after years of mismanagement, Cooper Union faced financial ruin. It announced that it would begin charging graduate students tuition — and possibly undergraduates, too. For months, with the support of activists from Occupy Wall Street, Cooper students held walkouts, sit-ins and noisy rallies. My students weren’t just fighting to keep their own education affordable. They were standing up for the principle of education as a public good.

I’ve been thinking about them a lot in recent months, even more so since Elizabeth Warren announced a plan for free public college and a partial debt jubilee, funded by “an ultra-millionaire tax.” A few days ago, Bernie Sanders introduced the College for All Act, which would eliminate all $1.6 trillion of the nation’s student debt and fund states and tribes to offer tuition-free higher education.

We will likely hear a lot of back and forth over the policy details during the Democratic primary race. Would the Sanders and Warren plans reach the neediest students? Wouldn’t debt forgiveness disproportionately help the middle class? Yet such criticisms, while well-intentioned, miss the emotional core of free college. The point, the red-hot sell, is that some things, like education, should be had by all — on equal terms. The debate over student debt is ultimately about our nation’s indefensible inequality.