In 1974, the American Psychiatric Association (APA) voted to delete homosexuality from its official list of mental disorders. In an official statement, the association declared, “Whereas, homosexuality per se implies no impairment in judgement, stability, reliability, or general social or vocational capabilities, therefore, be it resolved that the American Psychiatric Association deplores all public and private discrimination against homosexuals.” Many within the association believed that the statement would lead to improvements in the way homosexual patients were being treated. Gay rights activists—who had pressured the APA to change its official stance—heralded the change as a means of helping society accept gays and lesbians.

The majority of APA members believed that the organization’s new stance was supported by scientific evidence. The studies that the association had examined consistently showed that most gays and lesbians...