Now 56, Mr. Rudd’s stories from those tumultuous years of Vietnam protests, Black Panther ascendance and militant revolutionary zeal are so much better than your uncle’s rehash of drug-induced revelations and far-out cross-country road trips that they’ve become the subject of a new documentary, The Weather Underground, which opens June 4 at the Film Forum.

Mr. Rudd, who has lived in Albuquerque for 25 years now, returned to New York to see the show and publicly reminisce about his participation in the anti-war movement of the 1960’s.

As Mr. Rudd chattered amiably, it was hard to imagine this soft and jolly father of two, with his desert suntan and baggy chinos, at Columbia University in 1968. As a leader of the Students for a Democratic Society (S.D.S.), he helped stage a massive anti-war protest that shut down the school for two weeks and led to his dismissal.

In the film, Sam Green and Bill Siegel document how Mr. Rudd and several of his comrades went beyond instigating sit-ins in administrative buildings, founding a violent S.D.S. splinter group called the Weather Underground, which operated in the early 1970’s as a covert terrorist organization with the stated goal of inciting an armed revolution to topple the U.S. government.

The grainy footage of Mr. Rudd at Columbia and later in Chicago shows a young man with angular features, incongruously dreamy eyes and a mop of thick blond hair. Despite his tender years and relatively comfortable childhood—a Boy Scout and model student, Mr. Rudd was raised in upper-middle-class Maplewood, N.J.—he articulated a political agenda driven by anger and anchored in violence.

"We believed that there were no innocent Americans," Mr. Rudd later wrote in an unpublished memoir. "All Americans were guilty. All Americans were legitimate targets for attack. I was overwhelmed by hate, and I cherished my hate as a badge of moral superiority."

This hatred led the Weathermen to bomb dozens of U.S. government buildings and cause millions of dollars in damage.

By the mid-70’s, Mr. Rudd recalled, he had become convinced that violence was futile. He emerged from the underground in 1977, settled in New Mexico shortly thereafter and began teaching at Albuquerque Technical Vocational Institution in 1980. Since then, he’s been married twice, raised two kids, built his own house, and taught fractions and basic algebra to literally thousands of community-college students.

As a teacher, Mr. Rudd hasn’t strayed far from campus, but his take on the post-9/11 invasions of Afghanistan and Iraq is suffused with the same sardonic detachment one hears from many former hippies and peaceniks.

"We need a political movement in the Democratic Party that opposes a militaristic foreign policy," he said. "But it’s a hard struggle to be in the Democratic Party with this bunch of scumbags, opportunists, ego-freaks, maniacs and criminals.

"My dream ticket at this point is Oprah Winfrey on a peace platform with Bill Moyers as her Vice President; maybe Amy Goodman for National Security Advisor and Michael Moore for Secretary of Defense," he continued.

Mr. Rudd has aged so genially that it’s now nearly impossible to imagine this teddy bear of a guy ever penning manifestos like the now-famous open letter to the president of Columbia, Grayson Kirk, which concluded: "Up against the wall, motherfucker, this is a stick up."

Mr. Rudd has embraced pacifism; he hasn’t rioted in the streets or raged against the machine in years. But his politics still aren’t exactly mainstream.

"We still insist on denying the unpleasant reality that the reason this country exists on the level it exists is because of our conquest and exploitation of the whole world," he said, without the slightest hint of irony.

Mr. Rudd now operates in a more circumscribed political sphere: He works with the local teachers’ union and for environmental causes. He is a passionate advocate for changing the way math is taught in this country. The man who once orchestrated an attack against the head of New York City’s Selective Service, culminating with the colonel wiping lemon-meringue pie off his face, now gives passionate lectures at professional conferences with titles like "The Life and Hard Times of Developmental Math Reform at T.V.I."

Asked to account for his past, Mr. Rudd vacillates between playing the role of penitent and educator.

"Absolutely, I have feelings of shame. But I can forgive myself. I think it’s very hard to develop nonviolent discipline. Hitting back, especially when you’re 20 years old, feels great," he said. "In retrospect, I think I was probably driven somewhat crazy by the violence of the war in Vietnam, just like there are probably hundreds of thousands of young Muslim men being driven crazy by the violence today. We considered ourselves soldiers in a war against U.S. imperialism—and just like a soldier is willing to die for it, I was willing to die for it."