One fact: homosexuals cannot procreate. This means, if it is a genetic trait, it will have faded away into nonexistence... if you believe in natural selection which most Liberal/progressives do.
From a scientific perspective, it could be recessive. Still, I haven't read any credible studies that it is.
Actually, homosexuals can procreate if they are not exclusively homo in their behavior. Think of certain Congresscritters who were “happily married” with multiple children before they were caught one night going the other way.