I have always tried to argue that there is a very serious civil outcome to redefining marriage, and it has nothing to do with religious liberty or the idea of "sacramental marriage."
Since marriage is society's primary way of acknowledging and understanding parenthood, redefining marriage redefines parenthood. Here in California, the affects of "SSM" and redefining parenthood are rapidly making their way through the legislature. Last year, Gov. Brown signed a bill allowing three or more legal parents for children, which was inspired by a "SSM" custody dispute.
Now we have this: AB 1951. This bill will change birth certificates to allow for a gender-neutral option for parents. Gay couples will be able to list both of themselves on the child's birth certificate. California recently did away with the terms "husband" and "wife," because of "SSM," and the lead legislator for that measure said that those terms were outdated and biased. I suppose we can infer the same thing for "mother" and "father."
Contrary to assertions in certain quarters, these recent measures in California do not strengthen the idea of "family." On the contrary, measures such as these weaken the idea of "family," since the legal default for defining family is now based on an unreality. After all, biology says, "One father and one mother for a child."
Like a stake in the ground, reality limits the state, but the state must accept this reality. When the state embraces an unreality, as it has in "SSM," it has given itself a blank check to do a lot of other things.