"Again, I cannot comment on Mormon theology, but I am struck by how much this parallels the way orthodox Christianity sees marriage and metaphysics. We too believe that male-female marriage is an icon of God and His creative work, and that it cannot be represented any other way. What’s more, marriage is not simply a representation of divine nature, but also participates in it. In other words, complementary marriage (male-female) is really real, in a way that same-sex marriage cannot be. This is not a legal distinction (because same-sex marriage is a legal reality in many countries now), but a metaphysical one. Though orthodox Christians disagree deeply with Mormons over the nature of God, we share the belief eloquently expressed by Jacob Hess that to discard what the faith teaches about the nature of marriage as a way to participate in theosis, or metaphysical unity with God, is to lose something essential to the faith.
Again, based on what little I know about Mormon theology, the key point to take away here, re: orthodox Christian theology, is that both orthodox Christians and Mormons believe that marriage is not simply the name we give to a specific form of social relationship, but it is also something built into the fabric of reality. As Hess says, you don’t have to believe that story, but if you are going to understand why so many of us on the conservative side of this issue believe as we do, you have to understand that for us, to accept SSM is to deny something we believe is real. And that we cannot do."
It's always nice when people outside of Mormonism get it right. Make sure and read the entire article and consider sharing it: http://www.theamericanconservative.com/dreher/mormons-gay-marriage-benedict-option/