In March 2009, in Century City, Calif., four months after California voters passed Proposition 8 to ban same-sex marriage, political consultant Chad Griffin stood in a crowd of veteran gay activists and reeled from the hostility in the room. The ire was directed at the man onstage, screenwriter Dustin Lance Black, who had recently won an Oscar for “Milk,” about the gay activist Harvey Milk, who was assassinated in San Francisco in 1978.