HA, that is a very weak argument. I know MANY MANY gay people who grew up in Christian families. And I don't mean psuedo-Christians. Not the ones who go to church every sunday, pay lip service, and come home and forget it all. I mean real Bible-beleiving, Hardcore, Southern Baptist Christians. Those people were very damaged by the fact that they could not reconcile thier faith, and thier families, to what they were. I think you do a great disservice to your child by assuming his/her sexuality, and instilling him/her with derogatory and disrespectful attitudes about people who they might one day realize that they are. These people were not "damaged" by the fact they could not reconcile their faith, etc. They had no faith to begin with, so nothing to reconcile.
IF one of my children, or my step-son, were to come to me and tell me they were homosexual (NOT gay, HOMOSEXUAL), then they would not be welcome in my home until they CHOSE a better path in life. Cold? Too bad. If you embrace homosexuality, you are just as guilty in God's eyes.