ST. LOUIS, Nov. 13 - In one room, young gay activists were learning the basics of opposition research and analyzing the power of get-out-the-vote videos produced by evangelical groups. In another, the opponents of recent state amendments prohibiting gay marriage debated which strategies were more effective: Going door to door? Holding town hall meetings? Asking church congregations to give them an audience? About 2,500 organizers from gay groups across the country gathered for a conference here this weekend, the first large-scale gathering since the Nov. 2 elections, when voters in 11 states resoundingly approved amendments to their constitutions against same-sex...