Psychology initially studied homosexuality as an abnormal phenomenon. Until the 1970s, psychology/psychiatry viewed homosexuality as a pathology and a mental illness.
That classification began to be scrutinized by some researchers, they claimed that science failed to produce any empirical evidence or scientific basis for regarding homosexuality as a disorder or abnormality- based on their revised definitions of what was normal and abnormal and what constituted a mental disorder. It was also challenged by politically charged gay activist groups.
As a result of very limited, highly controversial and tainted research minor opposition to the the classification of homosexuality as a mental disorder arose. Some such as Dr. Nicholas Cummings one of the primary movers in having Homosexuality declassified as a mental Illness and author of the proposal to remove it from the DSM  made the following admission ...
'I made the resolution that being gay was not a mental illness, that it was character logical .... I also said with that, that the APA, if it passes this resolution, will also vote to continue research that demonstrates whatever the research demonstrates. Unbiased, open research.'
Dr Cummings, is a true scientist and a firm believer in Scientific Objectivity, which is a basis of all science, or at least its supposed to be.
Objectivity is a basic philosophical concept, related to reality and truth. Objectivity means the state or quality of being true even outside of a subject's individual biases. Scientific Objectivity is a value that informs how scientific studies are conducted and how scientific truths are arrived at. It is the idea that researchers, in attempting to uncover truths about the natural world, must aspire to eliminate personal biases, emotional involvement, etc . Today, it is nowhere to be found in the APA.
Scientific Objectivity has been swept under the carpet of convenience and completely forgotten. Since at least the Mid 90s leftist Ideology rules at the APA. Cummings has stated that its members are cherry picking results to fit their Agenda. As per Cummings 'the gay rights movement sort of captured the APA.' 
Altering The Facts for Political Convenience
The American Psychiatric Association declassified homosexuality as a mental disorder after years of political pressure from gay activists and under the limited weight of tainted and poorly implemented studies. The American Psychiatric association board of trustees passed this decision followed by a statement which listed among the reasons for their decision as changing social norms and growing gay rights activism . So basically, a scientific institution was coerced into changing a scientific opinion or classification due to political pressure and false evidence!?
In the early 1970s, the NGLTF staffed educational booths at American Psychiatric Association conventions and took an active role in lobbying the APA to remove homosexuality from its list of mental disorders. In 1978, it urged the U.S. Public Health Service to stop certifying gay immigrants as 'psychopathic personalities'. 
Beginning in 1968, homosexual activist groups began lobbying leading psychiatric organizations to lay the groundwork for the deletion of homosexuality as a mental disorder. From '68 till '72 while the APA Task Force [comprised entirely of homosexuals and homosexual activists] was actively preparing its report, any psychiatrist or psychoanalyst who dared to challenge them or present contradictory documentation anywhere in America was shouted down, heckled and in some cases even physically assaulted at meetings of mental health professionals.
If someone is born homosexual, the claim that he/she has no control over their perversion, the false assumption that their homosexuality is a product of their birth over which they have no control then why use the terms "sexual preference" or "alternative lifestyle"both of which imply that they have chosen their lifestyle.
The only scientific evidence cited when passing the resolution to declassify Homosexuality as a mental illness was based on studies by Alfred Kinsey, who admitted that he flubbed his results and Dr. Evelyn Hooker.
The Adjustment of the Male Overt Homosexual
Dr. Evelyn Hooker
Hooker, a professor at the University of California at LA is credited in the medical and psychological community, and most especially amongst Gay activists, with establishing that there is no measurable psychological difference between heterosexual and homosexual men. Her work proposed that homosexuality is merely a normal minority variation of human sexuality. Her 1957 study served as a basis for most of the later hyperbole of the Gay movements ideology, including the notion that any objection to the Gay agenda is born from an irrational fear, that they have since labeled "homophobia."
Her tainted study "The adjustment of the male overt homosexual" has long since been refuted and discredited by more recent and scientifically objective research.
In fact , even when it was initially presented Hooker herself conceded the possibility that homosexuals are indeed pathological, a point conveniently overlooked by the Gay Activists. That homosexuals are pathological has been proven out by later ,more reliable and objective studies.
Dr. Hookers work is covered more extensively in a separate article : Evelyn Hookers Bad Science
The removal of homosexuality from the American Psychiatric Associations Diagnostic and Statistical Manual of Mental Disorders was a serious mistake one of the voices that screamed this out at the time was Dr. Charles Socarides.
Voices of Reason
Charles Socarides , a prominent psychiatrist, psychoanalyst, physician, educator and author wrote that the removal of homosexuality from the American Psychiatric Associations Diagnostic and Statistical Manual of Mental Disorders was a serious mistake, and theorized that it contributed to the AIDS epidemic. He compared the gay community to confused children. Socarides claimed that the vote to delete homosexuality from the American Psychiatric Associations Diagnostic and Statistical Manual of Mental Disorders, was heavily influenced by pressure from gay activists, in particular a letter sent by the National Gay Task Force to 18,000 APA members asking them to support its removal.
The New York Times in 1995 stated "Socarides offered the closest thing to hope that many gay people had in the 1960s: the prospect of a cure. Rather than brand them as immoral or regard them as criminal, Socarides told gay people that they suffered from an illness whose effects could be reversed."  He theorized that homosexuality is a treatable neurotic adaptation.
Socarides wrote that classical male homosexuality generally develops in the first two years of life, "caused by a controlling mother who prevents her son from separating from her, and a weak or rejecting father who does not serve as a role model for his son ... "
Socarides reported that "about a third" of his patients became heterosexual after treatment. He taught Psychiatry at Columbia University and the State University of New York Downstate Medical Center, and was Clinical Professor of Psychiatry at the Albert Einstein College of Medicine, New York City, from 1978 to 1996.
APA Task Force Report -- a Mockery of Science
Dr. Nicholas Cummings
Nicholas Cummings was one of the primary movers in having Homosexuality declassified as a mental Illness back in the 70s.In fact, he wrote the proposal to remove it from the DSM.
Dr Cummings, is a true scientist and a firm believer in Scientific Objectivity, which is a basis of all science, or at least its supposed to be. As time progressed and more viable evidence proved homosexuality to be a mental malady, Cummings changed his stance and recanted his opinion that Homosexuality was not pathological. Cummings has stated that its members are 'cherry picking results' to fit their Agenda. As per Cummings the gay rights movement sort of captured the APA. See: : American Psychological Association Owned by the Gays.
Pro-Gay Laws Based on Fallacies
New Jersey has a law that prohibits juveniles from receiving counseling to overcome unwanted same-sex sexual attractions, behavior, or identity. This law could actually empower the state of New Jersey to remove children from their homes, and families if they attempt to thwart the homosexual agenda according to the bills sponsor. New Jersey Gay Democratic Assemblyman Timothy Eustace, called change therapy child abuse and proposed the government take away children seeking change from their parents. This law is modeled after a similar law in California  which has also been challenged. Pennsylvania, Washington State, Massachusetts, and the District of Columbia have introduced similar legislation.
Ninth Circuit Court of Appeals Upholds Ban on Change Therapy
Mat Staver Honored for Defending Freedom at Ex-Gay Awareness Dinner
NARTH _ National Assoc. For Research and Education of Homosexuality
Gay NJ lawmaker: We can take your children
References - Footnotes
1. Diagnostic and Statistical Manual of Mental Disorders (DSM) The Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the APA, offers a common language and standardized but politicized and at times non scientific criteria for the classification of mental disorders.
4. The section of this article dealing with Charles Socarides was adapted from Wikipedia - Charles Socarides
6. How America Went Gay - Charles Socarides.