Stanton L. Jones is provost and professor of psychology at Wheaton College. He writes in First Things:

Many religious and social conservatives believe that homosexuality is a mental illness caused exclusively by psychological or spiritual factors and that all homosexual persons could change their orientation if they simply tried hard enough. This view is widely pilloried (and rightly so) as both wrong on the facts and harmful in effect. But few who attack it are willing to acknowledge that today a wholly different, far more influential, and no less harmful set of falsehoods—each attributed to the findings of “science”—dominates the research literature and political discourse.

We are told that homosexual persons are just as psychologically healthy as heterosexuals, that sexual orientation is biologically determined at birth, that sexual orientation cannot be changed and that the attempt to change it is necessarily harmful, that homosexual relationships are equivalent to heterosexual ones in all important characteristics, and that personal identity is properly and legitimately constituted around sexual orientation. These claims are as misguided as the ridiculed beliefs of some social conservatives, as they spring from distorted or incomplete representations of the best findings from the science of same-sex attraction.

Today we approach same-sex attraction with views grounded in social and biological scientific perspectives that are only partially supported by empirical findings. Until the early decades of the twentieth century, moral disapproval of “sodomy” guided public policy, but that grounding was displaced by a psychiatric model that viewed homosexuality as a mental illness. Once homosexuality came to be seen not as a sin but as a sickness, it became a simple matter for social science to overturn the opposition to homosexual acts. Alfred Kinsey’s studies of male and female sexuality, published in 1948 and 1953, portrayed homosexual behavior of various kinds as a normal and surprisingly common variant of human sexuality. In 1951, Clellan Ford and Frank Beach published Patterns of Sexual Behavior, their famous study of diverse forms of sexual behavior, including same-sex behavior, across human cultures and many animal species; they suggested a widely shared “basic capacity” for same-sex behavior.

But the decisive blow to the mental-illness construal of homosexuality came from a single study in 1957. Psychologist Evelyn Hooker published findings that convincingly demonstrated that homosexual persons do not necessarily manifest psychological maladjustment. On the basis of Hooker’s work, and the findings of similar studies, in 1973 the American Psychiatric Association amended its designation of homosexual orientation as a mental illness.

To avoid misunderstanding the phenomenon of homosexuality, we must grapple with the Achilles heel of research into the homosexual condition: the issue of sample representativeness. To make general characterizations such as “homosexuals are as emotionally healthy as heterosexuals,” scientists must have sampled representative members of the broader group. But representative samples of homosexual persons are difficult to gather, first, because homosexuality is a statistically uncommon phenomenon.