Speech hurts. It creates ill feelings and even trauma in its victims. So, we need to enact rules and regulations to limit harmful speech, just as we do with littering, drunk driving or any other social hazard.

That’s been a common refrain of my fellow liberals in recent years, especially at our colleges and universities. And I agree with the first part: speech hurts. But once we use that fact to restrict it, almost anything can be censored. And one day, as I’ve been warning my left-leaning friends, the censors will come after you.

That day has arrived. More than 20 Republican-led state legislatures have considered laws this year to limit instruction about racism and sexism in public schools and universities. And of the five states that passed such measures by the end of June, several of them prohibited instruction that would give rise to “discomfort, guilt, anguish or any other form of psychological distress on account of the individual’s race or sex.”

Other schools have instituted regulations barring “threats” or “harassment,” which can apply to almost any speech that someone doesn’t like. California State University-Monterey Bay prohibits “any threat or action of physical, emotional, or verbal harm in any form.” At Northwestern University, an anti-harassment rule bars “offensive jokes related to a protected class.”

Who wants to harm or offend other people? I certainly don’t. So, grant the censors their due: these restrictions make a certain kind of sense. “Persecution for the expression of opinions seems to me perfectly logical,” Supreme Court Justice Oliver Wendell Holmes wrote a century ago. “If you have no doubt of your premises or your power and want a certain result with all your heart you naturally express your wishes in law and sweep away all opposition.”

But that sweeps away democracy itself, Holmes warned, which is premised on our ability to govern ourselves. What offends or harms one person might cheer or inspire another. Banning “offensive” speech allows the people with the most power to impose their definitions upon the rest of us, which squashes discussion of public questions that should concern everyone.

That’s what the new state laws try to do. Under the guise of protecting students’ psychological health, they effectively put difficult parts of our past and present — especially slavery and racism — out of bounds. Will addressing the Tulsa Race Massacre of 1921 or contemporary police brutality cause feelings of guilt or anguish in students? It’s hard to know, so teachers will avoid or downplay these topics. Happy faces only, please.