Why are you against the possibility that being gay might be at least partly genetic?
At one time it was popular even in some scientific circles to believe that when we are all born, our minds are a “blank slates” and that almost all of our behavior is learned. B.F. Skinner was one of the people who popularized this notion and claimed that if he had control of its environment, he could raise an infant to be almost anything he wanted. But we now know that this isn’t true. For example, not everyone, no matter how they are raised, can grow up to be a great musician. Some people have perfect pitch and this is probably genetic.
More recent scientific research has shown that many more of our abilities and our behaviors are influenced by our genes than what was once believed. But in most cases, what we become as adults is the result of a complex interaction between our genes and our environment. And there’s also epigenetics to take into account. Things that happen to us growing up can cause epigenetic chemical markers to be inserted over our genomes which can permanently change how our genes are expressed by permanently turning some genes on or turning others off.
Some conditions are caused by a single gene. Huntington’s disease is one of those as well as hemophilia. I have blue eyes and that is caused by a single mutation which first occurred about 10,000 years ago. Everyone in the world with blue eyes is most likely descended from this one person.
It’s important, however, to realize that most conditions or behaviors that have a genetic component are not going to be caused by one single gene. So, it’s unlikely that we will ever discover a single “gay gene” even if there is a genetic component to homosexuality. I have ADHD which definitely has a genetic component since someone who has a parent or sibling or other close family member with ADHD is much more likely to have it as well. But no single ADHD gene has yet been discovered. One ADHD expert says that a number of genes have been found in genome wide scans that appear to be associated with ADHD, but “even these associations are small and consistent with the idea that the genetic vulnerability to ADHD is mediated by many genes of small effect.” So, whether someone becomes gay could also be determined by an interaction between “many genes of small effect” with their environment both in utero and in growing up. The genes might not make someone gay, but they could predispose someone in that direction.