@TheArtfulDodger,
Isn't it obvious? The goal of marriage was never about protection of the children or about one man with one woman. The goal of marriage was to protect property right and to assure that the property could be passed down. Essentially, the quest for gay marriage is a quest for the same property rights. That is not the sole impetus but it is a large part of the reason why gays want to have legally recognized marriages.
BTW, the CHurch initially disapproved of marriage per se as a lifestyle choice. However, since marriage was necessary and since there was no civil authority over marriage, the early Church allowed couples to be married at the church door, never inside the sanctuary.
The CHurch was only stepping into the void: people demanded marriage and there was no civil authority to grant it.