Obvious, and perhaps doesn’t need to be said, but:
Whether homosexuality is genetic doesn’t affect my opinion of how homosexuals should be treated one iota. If two (or more) consenting adults want to do certain sexual acts in private, why exactly should I care?
In fact…I can’t for the life of me understand why some people are so intolerant of this phenomenon. Sure, some people cite religious reasons, but why focus so much on this teaching of the bible and ignore / re-interpret so many others?
Because it doesn’t require them to refrain from doing anything they enjoy. A lot of the other rules in the Bible, like “don’t eat shellfish”, would require these people to refrain from something they enjoy. “Don’t have gay sex” is an easy one to follow for most heterosexuals.
My thoughts are that your friend needs to learn the difference between “genetic,” “biological,” and “innate.” Hardly anyone argues that homosexuality is genetic. Some people do argue that it has a biological basis, and most everyone recognizes that it’s an innate characteristic. Of the three, the concept that homosexuality is innate is the only one that’s routinely used as an argument for gay rights, and even then, it’s neither the strongest nor the most common defence of the concept.
I don’t think genetic pre-disposition should make any difference in the debate. But rather than highlighting my own foundation, I focused on the given premises being used inconsistently. As to your questions, it seems to me that all behavior is at least biologically determined if not always predisposed genetically. But that leads quickly into a quagmire of a free will debate and the definitions of right, wrong, and responsibility.