Homosexuality
Younger generations might be surprised to learn that homosexuality was once seen as a mental illness. Additionally, from a professional position, rather than only in the sense of intolerance, that there are others who hold prejudices against the basic concept of homosexuality.
Long recognized as a real mental condition by mental health specialists everywhere, it was included in the Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association (APA) until 1973. All recognized mental conditions are listed and described in that manual. Only in 1990 was it removed from the World Health Organization's list of mental disorders.
Some believed that homosexuality was an immature person's way of being stuck in the heterosexual phase. Others believed it might have been brought on by a birth defect or exposure to a disease. According to a different theory, homosexuals just have the brains of people who identify as the opposing sex, which makes them attracted to the "wrong" sex.
Many treatments were explored, some of which were much more horrifying than others. Hypnosis and the use of reinforcement to coerce homosexuals into believing they were straight gave way to conversion therapy. The use of lobotomies and electroconvulsive therapy were two further, more harsh and cruel techniques. One medical professional "transplanted straight testicles" into castrated homosexual guys.