For $11 an hour I stocked nonfiction and worked the register at Black Oak Books in Berkeley, a used bookstore otherwise staffed by aging, garrulous intellectuals without institutional affiliation. For $12 an hour I assisted Sam Green, a filmmaker whose first documentary, The Weather Underground , chronicled the radical group from the 1960s responsible for bombing the US Capitol, the Pentagon, and the United States Department of State. The Weathermen always phoned their targets beforehand,…