There's 7 billion+ people in the world, only a small population are homosexual. How are they going to affect all 7 billion?
Way back when the human population was way lower it could have been considered a 'threat', but as we are now, homo-sexuality isn't an issue. Actually, even back then it wasn't an issue. Even if it was taboo, many leaders and iconical figures in history were gay. Take example the Spartans, they would throw away all their babies that had physical defects so that only the strong would live in their ranks, but guess what? When a male Spartan child gets old enough they get a sort of personal teacher that acts as a father for them, most of them had sexual relationships with each other. But was that a threat for them? No.
Also, stop throwing the 'natural selection' card as if it's proven. Nothing in science is proven, tests are made and theories are created that could best accurately depict the results to our understanding. That's the basic concept all scientists should know. No scientists can prove the Big Bang actually occurred, they can only assume, no scientists can prove Darwin's theory is correct. Science is built around theories and theories can never be proven, everything we know, from atoms, quasars to galaxies is ultimately a creation of humanity's imagination. Can you explain force? What it actually is; can you explain energy? No one can truly explain anything in science as science is all theory. THEORY.
You know what a theory is right? It's an idea that is created to give a better understanding of something. But theories are only 'ideas'. They are created by humans and can never be truly proven because as a race we are imperfect, and we always will be. Ultimately we can never prove what we know because it takes a higher being than humans to correct us. Take a child for example, when they do something wrong, who is the one that corrects them? Someone higher, an Adult. Which leads me back to the belief of God. You'd be surprised to know that the majority of scientists are believers of God even though science and religion have always butted heads since the creation of science. Albert Einstein is a brilliant example, and the reason they believe in God is because they know, they know that science can only be ultimately proven by a being higher than us. I'm not religious myself, I'm more inclined towards science, but having the same mindset as Einstein is what makes me hold onto the belief in God.