At first, AIDS appeared to be a disease of gay men. But by the time the virus responsible, HIV, had been identified a few years later, fear that sex, whether gay or straight, would kill millions of Americans shadowed every discussion of the topic. America’s sex life seemed poised for a dramatic change. But 25 years later, AIDS' true impact on the American sexual landscape has been muted, and, experts say, the changes that did occur were not always the ones we expected. Perception of what the sexual atmosphere was like before AIDS often relies on a convenient metaphor, like,...