You said:

I don't think that one of those doctrines is that gay sex within a marriage is a sin--and to the extent some leader said it was, I think he's wrong.

So the 15 "Church leaders" that signed the Family Proclamation are wrong? These aren't just random church leaders either.

THE FIRST COMMANDMENT that God gave to Adam and Eve pertained to their potential for parenthood as husband and wife. We declare that God’s commandment for His children to multiply and replenish the earth remains in force. We further declare that God has commanded that the sacred powers of procreation are to be employed only between man and woman, lawfully wedded as husband and wife.