The American population of third-trimester abortion providers declined by 20 percent in one terrible stroke in 2009, when Kansas physician George Tiller was murdered while attending his church. Martha Shane and Lana Wilson’s documentary acquaints us with the four remaining doctors left doing late-term abortions in this country, Tiller’s colleagues, all clearly rattled but resolved since his death to continue an already wrenching and unambiguously controversial practice. Withstanding vehement legal and geographic challenges, and protests both peaceable and violent, they grapple regularly with a complex moral dilemma, managing also to provide real support to their ever-desperate patients. (In some cases, they do turn patients away.) The film follows the doctors’ example, going about its grave task with compassion, basic professionalism, and discretion. It spends less time with opposers but cannot be said to neglect anti-abortion views: “This just feels like evil here,” says one prayerful man outside a clinic, and his words are at least enough to convey the true heartsickness on both sides of the debate. “Nobody fucking wants an abortion,” says Dr. Susan Robinson, as if the hardest thing, sometimes, is that she even has to say so at all. Of course Shane and Wilson’s attention is innately supportive, but it seems driven by humane curiosity and is by nature not an endorsement. What’s best about this unreservedly issue-driven film is its makers’ belief that between the preferred discourse polarities of silence and nasty noise, an alternative of actual conversation is possible.