Is Homosexuality a Choice?

At a debate focusing on issues important to the Lesbian, Gay, Bisexual, and Transgender (LGBT) community, Gov. Bill Richardson responded to a question on the nature of homosexuality. When asked by Melissa Etheridge if homosexuality was biological in origin or a choice, Richardson stated, "It's a choice."
Although he later retracted this statement (using the rather lame excuse that he misunderstood the question), it's puzzling to hear this line come from the mouth of Richardson. Opponents of gay rights often argue that individuals "chose" to be gay and therefore are not entitled to any special treatments. What is not addressed, though, is why some would make this choice?
Surely, a person wouldn't chose to be gay just to be denied rights, subject to societal scorn, and victimized in hate crimes. And if the choice was simply a choice of sexual partners, why wouldn't an individual chose to enjoy the full rights and privileges of a heterosexual and indulge in whatever sexual escapades he or she wished on the side? If homosexuality was merely a choice, any homosexual could have his or her cake and eat it too. But it's not.
Homosexuality is well known in the animal kingdom and is a biological fact of life.
If anyone thinks it's a choice, I'd like to hear the justifications of that view.