A mental disease.
Homosexuality (either by choice or genetic w/e in the brain) is maladaptive and doesn't further society. Mental diseases don't help people, it is something wrong in our head that makes us worse off (liberalism;)). If homosexuality isn't a disease how is ADD, schizophrenia, and anything else a mental disease?
Something is wrong, something needs to be fixed, we need to help them.
ADD and schizophrenia are proven medical conditions.
Being gay, in my mind, is more akin to how some people like sour candy and some people hate sour candy. There's no real reason why one person enjoys one flavour and another person enjoys another, it's just how they are.
If you're implying that liberalism is the same as homosexuality, then I think your point is more damaged than ever. Liberalism is nothing like homosexuality, a person makes a conscious decision about which, if any, political stance to take. Although I think that making that stance is stupid, that's besides the point. Homosexuals, on the other hand, don't have a choice. It's the same way I never chose to enjoy spicy food, it's just the way I am (nature or nurture? Well, I was never encouraged to like hot sause, and my parents certainly don't, so where else could it come from?)