Why are some people opposed to or even discriminating against homosexuality?

I remember I used to talk with my friends about homosexuality, but some of them do not understand why this will happen. And one of them even thinks this kind of person is not normal. I think the reason why they think so is related to our education. When I was a kid, we seldom talk about this kind of relationship, all we know from the book, our parents, or the movie was just a boy in love with a girl.

Some people discriminate against homosexuality because they think homosexuality obey nature. From a Darwinian point of view of evolution, homosexuality is indeed unnatural to some extent. Because most biologists agree that sex and desire are somehow biological adaptations designed to spread our genes. And homosexual sex does not transmit genes, which is against nature from this point of view.

But it is really wrong that some people obey nature?

Another reason that some people discriminate against homosexuality, maybe just they do not accept the difference that existed. And they think that what the general majority agrees is right. On the one hand, what I have seen and heard is different from the understanding given by my childhood education and growth environment, and I feel puzzled and rejected. On the other hand, I am afraid that this new difference will have a damaging effect on my existing interests. Suspicion, slander, swearing, disgust, and contempt, all began to gradually fill this heart, it is not surprising — so much that there is no intention to understand and recognize the difference. From the article, “Not just Florida. More than a dozen states propose so-called ‘Don’t Say Gay’ bills” they try to forbidden school discuss topic about sexual orientation.

So why are some people opposed to or even discriminating against homosexuality?