When teaching Political Philosophy to high school juniors in New York City, the author would spend evening hours pondering John Stuart Mill's treatise "On Liberty," asking herself how to help students through the difficult syntax and even more difficult ideas. Often, students would say at the outset that they agreed with Mill, but when pressed further, the author found more differences of thought. Indeed, the principles of liberty that Mill articulates--first, that all opinions have a place in public discussion, and second, that people should be allowed to live as they wish, as long as they do not impinge on others' rights--are so far from general acceptance today that liberty itself, or at least Mill's conception of it, remains a distant aspiration. Building it would require not only great dedication but also fear of the alternatives.