Okay. I guess I'll start with the APA (American Psychological Association) which is by far the largest and most influential mental health organization in the US, as well as being the largest in the world. Here is a link to dozens of peer reviewed articles that discuss homosexuality, as well as statements by the APA in regards to homosexuality. In short, they say that gay people are not "bad", their sexuality cannot be changed, they make effective citizens and gay couples should have the same rights as straight couples.
APA Policy Statements on Lesbian, Gay, Bisexual and Transgender Concerns
Ditto to the other top five largest scientific mental health organizations in the US.
Heres the opening sentence in the largest ever research study to determine the origins of sexual orientation - ""It builds on previous studies that have consistently found evidence of genetic influence on sexual orientation, but our study is the first to look at exactly where those genes are located," says researcher Brian Mustanski, PhD, a psychologist at the University of Illinois at Chicago."
Let me know if you want more.