I wrote this many years ago and have posted it many times. It’s still relevant:
There is no genetic test or procedure (experimental or otherwise) that can determine one’s sexual orientation. When people claim to be gay and we believe them, what we’re really doing is taking them at their word. We believe their claim, we believe their testimony and we believe their declaration that they are gay.
But there are some people who are suddenly skeptical when one claims to be ex-gay. They don’t believe the ex-gay claim, they don’t believe the ex-gay testimony nor their declaration that they are ex-gay.
When somebody uses a certain standard to measure the credibility of what one group says, but then refuses to use the same standard to measure the credibility of what another group says—thereby ignoring the claims of the second group (ex-gays)—he should ask himself why he believes one group and not the other... This is a double standard.