There is actually a theory about this, claiming that the unborn baby is infected by a virus which causes the condition in adulthood. Neither side of the chasm wants to talk about this theory, however:
I harp on this point every time this comes up but I’ll say it again, a disease is a disease, all kinds of diseases are genetic, “born that way”, so what? Totally irrelevant.
Homosexuality is aberrant and unhealthy, a disease that should be treated not a “character trait” that should be celebrated, no matter what causes it.