If Allah allows abnormal gay boys to be born so why homosexuality is a sin?
A lot of muslims claim that homosexuality is a sin because it is unnatural. I disagree with them. Homosexuality has been observed in many animals. So it's completely natural. HOWEVER, it's still a sin. Just because something is natural does not mean that it will not be haram. For example, cannibalism is also natural. Does that mean it is halal to eat other human beings? No. So why is homosexuality haram? Allah knows best.
But if I really had to come up with an answer to why homosexuality is haram, it is this: Allah chose us (human beings) over all other animals. So he expects us to live our lives in a way different from other animals. That's why he made special laws for us to abide by. This is my best guess to why homosexuality is haram.
Another thing you should know is just because a person is a homosexual doesn't mean that he/she is guaranteed to go to hell. As long as the homosexual person doesn't act upon his desires and lives the life of a normal muslim, he/she has nothing to worry about. If a person is born a homosexual, that means Allah is testing him/her. He can either give in to his homosexual urges and be like the animals OR he could follow the laws Allah made unique for human beings.