Dr Roger Harris, now a distinguished educator and a clinical assistant professor at Boston University, grew up in Roxbury. As a teenager, some of his peers tried to entice him to join a gang. But he chose the life of a different kind of “gladiator,” as he put it — he became a Marine. He served for three years and spent 13 months fighting in the war in Vietnam. Harris talks to WGBH’s Bob Seay about how he became involved in Ken Burns and Lynn Novick's "The Vietnam War" documentary, his experience, and what we can learn from the film.