His successor, Russell Moore, sounded a different note when the Supreme Court in June struck down the federal Defense of Marriage Act. "Love your gay and lesbian neighbors," Mr. Moore wrote in a flier, "How Should Your Church Respond," sent to the convention's estimated 45,000 churches. "They aren't part of an evil conspiracy." Marriage, he added, was a bond between a man and a woman, but shouldn't be seen as a "'culture war' political issue."

Since the birth of the Christian-conservative political movement in the late 1970s, no evangelical group has delivered more punch in America's culture wars than the Southern Baptist Convention and its nearly 16 million members. The ...