Henry Allen, who won the Pulitzer Prize for criticism in 2000, was a Post editor and reporter for 39 years.

“It’s a glamour issue,” said Michigan factory worker Dave Van Dam. “The kids come in here and see a dirty, loud place.”

He was explaining the shortage of skilled factory workers in America, as reported this week in The Post. One of the causes is “the stigma of factory work.”

I understand. I did stand-up factory work when I was in college: hand-riveter, degreaser, bucket man on an automatic screw machine. I hated it.

It was not only dirty and loud, it was also becoming contemptible then, in the age of Kennedy, who removed the ivory-tower stigma from intellectuals and made them cool, enfranchising them (and me, the college boy) as the rightful rulers of America. “Brains,” he said. “You can’t beat brains.”

A new class was born. Leading it were people such as Harvard’s Robert McNamara, Kennedy’s defense secretary. We were thrilled when a story went around that he had interrupted a slide show at the Pentagon to point out that Slide 347 was the same as Slide 51, or numbers to that effect. Surely, here was the avatar of intelligence, which would save the world.

The new class talked about intelligence as if it were a moral virtue along the lines of courage or patience, even though intelligence is only a tool with no more moral virtue than a crowbar. Acing the SATs became tantamount to sainthood.

The country seemed seized by the glamour of brains. Working-class heroes vanished from television sitcoms. By 1971, Ralph Kramden, Jackie Gleason’s big-hearted bus driver in “The Honeymooners,” would become Carroll O’Connor’s Archie Bunker, the blue-collar bigot.

An essay published by the Museum of Broadcast Communications said: “The movement of working-class people to the periphery of television’s dramatic worlds” in favor of the upper classes gave “the impression that those not among these classes are deviant.”

The impression remains, as contempt or condescension. Here’s Walter Russell Mead, a noted policy scholar, saying in a recent blog posting that revolutions in information technology create “the potential for unprecedented abundance and a further liberation of humanity from meaningless and repetitive work.”

I’d thought these revolutions had liberated stand-ups from this work by throwing them out of it, but what caught my eye was the “meaningless and repetitive.” What an odd thing to say — Mead might just as well be describing what it’s like to be a stockbroker or a big-firm lawyer. He isn’t, though, because these are knowledge-class jobs, and this rap about “meaningless” is usually reserved for the stand-up class.

Not long after Kennedy, grumbling began from the deviant stand-ups about “pointy-headed intellectuals.” Meanwhile, the pointy heads got phobic about the stand-ups, as if they were zombies lumbering toward their campuses with shotguns.

In the 1969 movie “Easy Rider,” a knowledge-class favorite, the hippie motorcyclist heroes are shotgunned by a man in a pickup truck. In 1970’s “Joe,” a stereotype of a factory worker slaughters counterculture types.

Ugly stuff. Things could get ugly indeed in civil rights battles, or with the drunk construction workers I saw rampaging through Wall Street one day, beating up war protesters. There was something to fear all right.

It didn’t turn out to be their shotguns, though, as much as their votes. They tended to give them to conservatives who turned liberal intellectuals into a dispossessed aristocracy, one that regarded Ronald Reagan as a mere aberration before the restoration of Camelot, which never came.

Except they’re not really aristocrats; they’re a caste.

The difference is, an aristocracy feels obligated to those beneath it (however ill-observed), whereas a caste protects its own privileges, like McNamara sending stand-ups to Vietnam while confiding to Kennedy staff historian Arthur Schlesinger that he knew we couldn’t win. He thereby demonstrated he was smarter than they were while knowing his secret was safe.

It isn’t just Democrats and liberals, I should point out. It took the brilliance of Paul Wolfowitz, PhD, to concoct the Iraq war by finding weapons of mass destruction that didn’t exist. As with McNamara, he would go on to be rewarded with the presidency of the World Bank.

For the liberals now, we have Barack Obama, with full knowledge-class creds. Talking about the stand-ups in 2008, he didn’t condescend — he outright pitied them, which is worse: “They get bitter, they cling to guns or religion or antipathy to people who aren’t like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations.”

In my last factory job, making tile at the Armstrong Cork Co. in Lancaster, Pa., I was loafing one day, sitting on a pile of boxes. Some of the guys from the adhesives ovens came walking past, big guys in filthy coveralls.

One of them said: “What the hell do you think you’re doing?”

I made up something like, “I’m waiting for a forklift.”

He didn’t care about me loafing. It was something else.

He said: “You don’t ever sit down when you work. Ever.”

He was proud to work standing up. Until that moment, I hadn’t understood that pride, and the virtue of that pride.

I’m glad we have people who do, people who take pride in being able to do “meaningless” jobs, to support families and pay debts by sticking to their work, to discipline themselves into persistence, to endure.

These are moral virtues. I wish the knowledge class was smart enough to respect them. It seems we need them.