Fifty years ago, every state criminalized homosexual sex, and even the American Civil Liberties Union did not object. The federal government would not hire people who were openly gay or permit them to serve in the military. Police routinely raided gay bars. Only a handful of gay-rights organizations existed, and their membership was sparse. Most Americans would have considered the idea of same-sex marriage facetious. Today, opinion polls consistently show a majority of Americans endorsing such marriages; among those aged 18 to 29, support is as high as 70 percent. President Barack Obama has e...