No, I don't think that I am agreeing with you. Just because an infant does not express a sexual attraction towards either the same or the opposite sex does not mean that they do not possess an inborn sexual orientation.
This works both ways. You cannot legitimately claim that homosexuals do not have a same-sex attraction until later in life.
You need to do some research because there have been a number of documented cases of animals that are, in fact, 100% homosexual without ever being interested in a member of the opposite sex. Sexual orientation is NOT "invented"...it simply is a part of life.
I remember reading about a captive condor breeding program in which the scientists tried unsuccessfully to get two male condors to mate with females. These males simply would not mate with females, but stayed as a bonded pair. Initially, the scientists thought that the loss of two breeding males would negatively impact the breeding program, but they eventually decided to allow these two males to remain as a couple, and they gave them fertilized eggs from heterosexual pairs to brood and raise the chicks.
The "uncles" turned out to be great parents to their adopted chicks, and the heterosexual pairs simply laid more eggs that they raised, so that the program benefited greatly.
There have also been similar 100% homosexual pairs of various animals that have been observed. NONE of these pairs EVER engaged in heterosexual sexual relations.
Being born with a homosexual orientation from birth most definitely DOES affect your arguments against homosexuality. If a person or animal is born with a specific sexual orientation, that makes it perfectly normal even if such humans or animals are not in the majority, and declaring them "sinful" or "useless" or "detrimental to society" and something that should be "eliminated" makes YOU the sinner--not them.