This latest documentary from the Berkeley-based producing-directing (and wife-husband) team of Catherine Ryan and Gary Weimberg has a deceptively straightforward premise: “This film is about killing in war,” we learn early on from Peter Coyote’s narration. “And about some U.S. soldiers who have chosen not to.” As its title suggests, Soldiers of Conscience grapples with an apparent moral contradiction. It asks the questions we have presumed that decency forbids, and tests a counter-intuitive hypothesis that the call of military duty need not be dehumanizing by default. This involves chillingly intimate recollections from a handful of conscientious objectors, each rather astonishingly articulate, and from veterans who’ve taken lives without hesitation and will again if so required. It’s a modest, unpretentious film, and probably more affecting for it: Conveying not just the grimly harrowing circumstances of modern combat but also a real sense of the bright, mature and morally serious minds that terrible crucible has forged, Soldiers of Conscience amounts to a timely cross-examination of the human killer instinct.