As the coronavirus continues to spread, the chances that any one of us will be placed in quarantine goes up considerably. I know that being locked away like that would drive me nuts. Two weeks subtracted from my life! Still, I’d accept the justice of my confinement because I would recognize that my liberty had come to pose a real danger to my fellow humans.

Now, let’s ratchet up the sacrifice: Suppose you were required by law to turn the thermostat up to 75 in the summer, and down to 66 in the winter, in order to reduce your carbon footprint. The principle is the same: Your freedom to live as you wish turns out to jeopardize public well-being. I, for one, would bristle; I can’t stand being hot in summer. Maybe you wouldn’t mind. But what if you were also told that you had to eliminate most or all of the red meat from your diet? What if Greta Thunberg persuades President Sanders that we need to ration jet travel? At some point you’ll begin to think that the increasing globalization of bad things like climate change and infectious diseases is threatening liberal society.

You’d have a point. At the foundation of classical liberalism is John Stuart Mill’s principle that every individual must be free to speak and act as he wishes “so long as he refrains from molesting others in what concerns them, and merely acts according to his own inclination and judgment in things which concern himself.” For instance, drinking to excess, Mill said, deserves reprobation, but not prohibition; it’s a self-regarding act. But there’s a problem with this formulation: Even in his own time Mill was criticized for drawing a largely artificial distinction between behavior which does and does not impinge on others. The filaments that bind people to one another are incomparably stronger today than they were in Victorian England. What would Mill have said if England had had then, as it does now, a public health system in which everyone shared the cost of treatment for alcoholism? What would he have said about smoking if he knew about the effects of secondhand smoke? Indeed, secondhand smoke is rapidly becoming a metaphor for our time.

I first started fretting over this question a few weeks ago, when I went to a Manhattan high school where I serve as a volunteer writing tutor. I was working with a young woman who had written an essay weighing the evidence that we could reduce global warming by switching to a vegetarian or vegan diet. She had learned that, thanks to the methane and nitrous oxide released by cows and manure, livestock is responsible for as large a fraction of CO2 emissions as the entire transportation sector (including air travel) — about a seventh. (In fact, the figure for livestock includes, among other things, the emissions caused by transporting meat and dairy products, which properly belongs under transportation.)