Being gay is a choice.
There are actually two underlying statements.
1. Having homosexual feelings is a choice.
Despite scientific evidence to the contrary, many ex-gay organizations now try to insist that while one doesn't choose an orientation it can be changed. They don't want to admit there is a biological component because that is less likely to be changeable. They still insist being gay is a result of a psychological trauma (the old missing father claim).
The ex-gay industry has not done long-term studies to show the effectiveness of their therapy. But why should the source of an orientation matter? Why should gays be asked to change? The only answer is social pressure.
This belief in choice doesn't just make the ex-gay industry possible, it also fuels a very large part of the animosity towards gays summed up in the phrase, "Save the children." But if homosexuality isn't a choice there is little to save the children from (alas, the bogus gay = pedophile claim is still out there).
Gays sometimes counter that if being gay were a choice then no one would choose to be gay. Why do we portray our lives as being so awful?
The better response is to say America allows choices in all areas of life -- including religion. So what if orientation is also a choice?
Being gay is no more a choice than skin color. So if blacks could change their skin color and didn't it would be acceptable to discriminate against them? Racism is wrong because there is nothing wrong with being black.
Why must gays change when the bad things associated with gay sex apply equally to straight sex? Why are only gay rights restricted when those bad things happen?
Sexual orientation has no bearing on whether and how well a person contributes to society. Unrealistic social pressures and outright discrimination does affect productivity.
2. Engaging in homosexual acts is a choice.
The anti-gay industry still hasn't shown why it is wrong for gay people to express themselves sexually in ways similar that straight people do -- other than using religious arguments. Perhaps they are uncomfortable with the human body in general.
Our opponents assume all gays indulge in the "gay lifestyle" of all night drunken group sex that leads to AIDS. But that isn't required of gay people, who also form stable relationships, any more than it is required of straights to take part in sex clubs (which some most certainly do).
The claim is that you either live a morally upright straight life of descend into a wretched gay life of sex, drugs, disease, and death. Faulty choice. The choice is between living a lie and not. Yes, gay behavior is a choice. It is false to assume that choice must be bad.