If your child is a thief, an adulterer or a murderer, he will be harming someone else. If he's gay, that isn't necessarily so.
Very poor argument on your part.
Nope...you miss the point. You don't change, or diminish, Biblical teaching because of something happening in your family.
The Word of God doesn't change to fit your needs. You change to fit the Word of God.
The issue is not harm to others but harm to himself, including not only the actual anatomical harm of the acts that gay men engage in, but also the threats of disease that accompany the unregulated promiscuity that exists between men. Then there’s the social stigma that comes by virtue of being in a very small minority, a minority that is deemed by most as abnormal (not to be confused with acceptable).