“Freedom of speech,” the famous Norman Rockwell painting that depicts a young man addressing a local gathering, was inspired by a real event. One evening in 1942, Rockwell attended the town meeting in Arlington, Vt., where he lived for many years. On the agenda was the construction of a new school. It was a popular proposal, supported by everyone in attendance — except for one resident, who got up to express his dissenting view. He was evidently a blue-collar worker, whose battered jacket and stained fingernails set him apart from the other men in the audience, all dressed in white shirts and ties. In Rockwell’s scene, the man speaks his mind, unafraid to express a minority opinion and not intimidated by the status of those he’s challenging. He has no reason not to speak plainly: His words are being attended to with respectful attention. His neighbors may disagree with him, but they’re willing to hear what he has to say.

What brings Rockwell’s painting to mind is a new national poll by the Cato Institute. The survey found that self-censorship has become extremely widespread in American society, with 62 percent of adults saying that, given the current political climate, they are afraid to honestly express their views.

“These fears cross partisan lines,” writes Emily Ekins, Cato’s director of polling. “Majorities of Democrats (52 percent), independents (59 percent), and Republicans (77 percent) all agree they have political opinions they are afraid to share.” The survey’s 2,000 respondents sorted themselves ideologically as “very liberal,” “liberal,” “moderate,” “conservative,” or “very conservative.” In every category except “very liberal,” a majority of respondents feel pressured to keep their views to themselves. Roughly one-third of American adults — 32 percent — fear they could be fired or otherwise penalized at work if their political beliefs became known.

Freedom of speech has often been threatened in America, but the suppression of “wrong” opinions in the past has tended to come from the top down. It was the government that arrested editors for criticizing Woodrow Wilson’s foreign policy, made it a crime to burn the flag, turned the dogs on civil rights marchers, and jailed communists under the Smith Act. Today, by contrast, dissent is rarely prosecuted. Thanks to the Supreme Court’s First Amendment jurisprudence, freedom of expression has never been more strongly protected — legally.

But culturally, the freedom to express unpopular views has never been more endangered.

On college campuses, in workplaces, in the media, there are ever-widening no-go zones of viewpoints and arguments that cannot be safely expressed. Voice an opinion that self-anointed social-justice warriors regard as heretical, and the consequences can be career-destroying. The dean of the nursing school was accused of being a racist and forced to quit for saying that his museum would “continue to collect white artists.” The director of communications for Boeing apologized and resigned after an employee complained that 33 years ago he was opposed to women serving in combat.

Virtually everyone would agree that some views are indisputably beyond the pale. If there are supporters of slavery or advocates of genocide who feel inhibited from sharing their beliefs, no one much cares. But the range of opinions deemed unsayable by today’s progressive thought police extends well into the mainstream. And in many cases, the most enthusiastic suppressors of debate are students, journalists, artists, intellectuals — those who in former times were the greatest champions of uninhibited speech and the greatest foes of ideological conformity.

It isn’t only on the left that this totalitarian impulse to silence dissent exists. President Trump, always infuriated by criticism, has called for columnists who disparage him to be fired, hecklers at his rallies to be beaten up, and TV stations to lose their licenses if they run ads vilifying his handling of the pandemic — calls routinely amplified on social media by tens of thousands of his followers. When a Babson College professor joked that Iran ought to bomb “sites of beloved American cultural heritage” like the Mall of America and the Kardashian residence, a right-wing website launched a campaign that got him fired.

The new Cato survey found that more than one in five Americans (22 percent) would support firing a business executive who donated money to Democrat Joe Biden’s presidential campaign, while 31 percent would be OK with firing someone who gave money to Trump’s re‐election campaign. The urge to ostracize or penalize unwelcome views isn’t restricted to just one end of the spectrum.

Americans’ right to free speech is shielded by the Constitution to a degree unmatched anywhere else. But our First Amendment guarantees will prove impotent if the habit of free speech is lost. For generations, Americans were raised to see debate as legitimate, desirable, and essential to democratic health. They quoted Voltaire’s (apocryphal) aphorism: “I disapprove of what you say, but will defend to the death your right to say it.” Editors, publishers, satirists, and civil libertarians took to heart the dictum of Supreme Court Justice Oliver Wendell Holmes Jr., who wrote that “the principle of free thought” is meant to enshrine “not free thought for those who agree with us but freedom for the thought that we hate.”

But that principle has been turned on its head. The “thought that we hate” is not tolerated but stifled. It is reviled as taboo, forbidden to be uttered. Anyone expressing it may be accused not just of giving offense, but of literally endangering those who disagree. And even if only some people lose their careers or reputations for saying something “wrong,” countless others get the chilling message.

“And so dread settles in,” writes journalist Emily Yoffe. “Challenging books go untaught. Deep conversations are not had. Friendships are not formed. Classmates and colleagues eye each other with suspicion.”

And 62 percent of Americans fear to express what they think.

The speaker in Norman Rockwell’s painting may have had something unpopular to say, but neither he nor his neighbors had any doubt that it was appropriate for him to say it. Now, such doubt is everywhere, and freedom of speech has never been more threatened.

(Jeff Jacoby is a columnist for The Boston Globe).