In the eyes of the radical Left, sexuality is as immutable as skin color, and thus to disagree with homosexuality is as bad as racism. Now, for the moment, we will ignore how offensive this is to actual victims of racism. Instead, let's talk about the very dangerous door the "born that way" argument opens.
Skin color genuinely is an immutable trait. You are born with a certain amount of melanin, and that gives you the very obvious appearance of being a very specific color. You cannot "do black". You cannot "act white". Black and white (which are actually just varying shades of brown) are all visible traits. You can tell what color someone is as soon as they are born.
But can you tell their sexuality? No, you cannot. This is because sexuality, far from being a trait, is a behavior. A behavior which I am not going to describe as I just did with skin color, but it is nevertheless a behavior.
But so is homophobia. This gives Leftists a choice. They must either acknowledge that homosexuality is a choice, and is therefore a choice for which we will be held accountable, or they must claim that other behaviors, such as homophobia, are just as natural as homosexuality, and thus a homophobe is no more responsible for their actions than a gay person is for theirs. At the very least, they must acknowledge that even if we are born with a tendency towards a specific behavior, we ought to control ourselves with regard to it.
As a Christian, I acknowledge that both homosexuality and homophobia are sins. It is wrong to abuse our bodies by deviating from God's design, and it is wrong to abuse other people for their sins. The good news for both kinds of sinners is that Jesus loves them both. Jesus is neither a homophobe, nor a homophobeophobe. Rather, He went to the cross in order for both types of sinners to be able to inherit eternal life.
You cannot be born gay, or homophobic, but we are all born in sin. But Jesus tells us very firmly: be born again. This requires repentance. Stop treating ourselves, and other people, as mindless animals. We do have a choice. And we will be held accountable for the choices we make. Repent or rebel, your genes don't determine that for you.