Author of the million-copy-selling A People’s History of the United States, 81-year-old Howard Zinn is the activist academic as working-class hero. This affable, craggy professor has an unmistakable voice—he’s the embodiment of Depression consciousness and urban Jewish poverty projected into the social struggles of the ’60s. A onetime longshoreman, Zinn found his first teaching job at Spelman College, a school for black women in Atlanta, and thus was a participant in, as well as a historian of, the civil rights movement. Fired for his activism, Zinn landed at Boston University in 1964, just in time to speak out—and not for the last time—at Boston’s first mass rally against the war in Vietnam. Teaching again merged with political action, most spectacularly when Zinn accompanied Tom Hayden to Hanoi to bring home three released P.O.W.s.

You Can’t Be Neutral on a Moving Train, which takes its title from Zinn’s recent memoir, provides the historian with a platform to address the Afghan and Iraqi wars. But Deb Ellis and Denis Mueller’s fond portrait, less documentary than infomercial, is unrelentingly and in the end self-defeatingly positive—albeit effective in showcasing Zinn’s charismatic personality. The pop-star ambience is enhanced by Matt Damon’s voice-over narration. Damon not only grew up next door to Zinn in Cambridge but gave A People’s History a mighty plug when he recommended it to his therapist, Robin Williams, in Good Will Hunting: “This will knock you on your ass.”