From Science Daily:
"There is no valid scientific basis for denying same-sex couples the right to legal marriage, or to deprive them of considerable benefits of the institution, according to legal briefs filed with the U.S. Supreme Court by the American Psychological Association and other leading mental health associations."
"The briefs cite empirical scientific evidence that demonstrate that "homosexuality is a normal expression of human sexuality, is generally not chosen and is highly resistant to change." Likewise, "there is no scientific basis for concluding that gay and lesbian parents are any less fit or capable than heterosexual parents, or that their children are any less psychologically healthy and well-adjusted," according to the briefs."
"Joining APA in filing the Windsor and Perry briefs were: the American Academy of Pediatrics; American Medical Association; California Medical Association; American Psychiatric Association; American Psychoanalytic Association; and National Association of Social Workers. Also joining the Windsor brief were: the New York City and New York state chapters of the National Association of Social Workers and the New York State Psychological Association. Also joining the Perry brief were the American Association for Marriage and Family Therapy; the California Chapter of NASW and the California Psychological Association."