How do you know? Just curious. Is it even possible to prove what you just said?
"Yet people are born sterile. People are born with deformities. People are born autistic. These are all detrimental to survival yet demonstrably these people are born all the time. So, either God is doing that, or evolution is but it works out the same in the end, it is happening.
Now, why can't people be born gay? You call it a mental disorder. Fair enough. Why can't people be born with a mental disorder"
I'm going to use your response to maluca to answer:
Yes people are born with imperfections but they are not sinful. To engage in homosexual acts is a sin, therefore there is choice involved. You either perform the act or you deny the act.
It would be the same for a heterosexual to have an adultrous sexual relationship. They weren't born "that way", they chose to sin.
And in my opinion, it is not a mental disorder, but it is a weakness of the flesh.