Figuring out of what's the opposite of what is one of those Sesame Street skills that doesn't often get practiced in a critical thinking or logic course.  You get a little of this in the logic of terms if you cover obversion or contraposition.  It's a useful skill, I think, just ask Tony Perkins.  Speaking of the Federal judge who decided the recent Proposition 8 case in California, he says:

"Had this guy been … an evangelical preacher in his past there would have been cries for him to step down from this case," he added. "So I do think [his homosexuality] has a bearing on the case. But this is not without precedent."

The logical complement of "homosexual" is not "evangelical preacher."

Besides, on this argument,  a married or marriable straight person would stand in the same allegedly biased relation to the outcome as a single gay person.  Who does that leave?