“Dallas Buyers Club” features two of the most powerful acting performances of the year and a handful of deeply moving scenes. Yet the dominant feeling it left me with was ambivalence, because for each of its strengths, there is at least one flaw that undercuts the film’s power. Based on a true story, the film chronicles the struggles of Ron Woodroof (Matthew McConaughey), a drug-abusing, womanizing, gay-hating electrician and bull rider whose life is upended when he is diagnosed with AIDS. The film is set in 1985, when most people, especially homophobic rednecks like Ron, believed AIDS was a disease that only struck homosexual men.