Let's see if anybody knows...
(I do but let's see some gay agenda lovers' answers first)
Hint: tell us about how much science was involved in the removal

In 1952, when the American Psychiatric Association published its first Diagnostic and Statistical Manual of Mental Disorders, homosexuality was included as a disorder. Almost immediately, however, that classification began to be subjected to critical scrutiny in research funded by the National Institute of Mental Health. That study and subsequent research consistently failed to produce any empirical or scientific basis for regarding homosexuality as a disorder or abnormality, rather than a normal and healthy sexual orientation. As results from such research accumulated, professionals in medicine, mental health, and the behavioral and social sciences reached the conclusion that it was inaccurate to classify homosexuality as a mental disorder and that the DSM classification reflected untested assumptions based on once-prevalent social norms and clinical impressions from unrepresentative samples comprising patients seeking therapy and individuals whose conduct brought them into the criminal justice system.
In recognition of the scientific evidence,[150] the American Psychiatric Association removed homosexuality from the DSM in 1973, stating that "homosexuality per se implies no impairment in judgment, stability, reliability, or general social or vocational capabilities." After thoroughly reviewing the scientific data, the American Psychological Association adopted the same position in 1975, and urged all mental health professionals "to take the lead in removing the stigma of mental illness that has long been associated with homosexual orientations." The National Association of Social Workers has adopted a similar policy.
Thus, mental health professionals and researchers have long recognized that being homosexual poses no inherent obstacle to leading a happy, healthy, and productive life, and that the vast majority of gay and lesbian people function well in the full array of social institutions and interpersonal relationships.[2]