“Scientific knowledge of the mind is expanding all the time. In the past, psychiatry viewed homosexuality as a mental illness. Knowledge of sexuality has improved markedly and we now recognise that homosexuality is not an illness to be cured. Moreover, there is a growing body of research suggesting that gay and lesbian people can experience benefits to their mental health and well-being if their relationships are given the same social and legal recognition as heterosexual relationships. From a mental health standpoint, the benefits of marriage should be made available to all couples regardless of the gender of the partners.” (Aug 2011)
Research into the health and well-being consequences of denying same-sex attracted people the right to marry can be found at the Doctors for Marriage Equality web site.