Let me clarify: this is not a question of motive. It's a question of the internal logic of the position being promoted. The main motive here is to elevate the status of gay people and their relations to the same social and legal plane as opposite-sex married ones. But let's play with that logic and see where it takes us.
Let's take the Loving v. Virginia analogy seriously. People who believe that there is something unique and important about unions of husbands and wife (like say they can make babies that the child's own two parents will raise together) are like bigots who opposed interracial marriage. People like me who have been working for 15 years against the family diversity advocates to call attention to the fact that "children need mothers and fathers" are like bigots who oppose interracial marriage.
If like me you think renewed attention to the problem of generativity is the key to saving Western civilization, this has got to worry you.
Now of course some advocates of SSM (Andrew Sullivan) say this change has already taken place. People like me are living in a fantasy world. All I can say is, I've been out in the world quite a lot saying this, and find that far from a fantasy it still has enormous power and resonance. So using law to discredit it, or stigmatize it, or just embarrass people who believe it and work to strengthen this connection, is likely to have a real impact on real children. Marriage as a cultural idea that has social power doesn't just happen. The law doesn't create it. Families and faith communities do, primarily, supplemented by artists, lawyers, counselors etc. Telling the big chunk of people at work trying to strengthen the idea that children need moms and dads they are officially now bigots, is well, its going to make this work a lot harder and less effective. Probably impossible
Other advocates of SSM acknowledge that SSM will change these things, but these changes won't matter, because we will still be able to say "marriage is good for children." It is just of course the underlying logic and rhetoric will shift.
In the new dispensation, socially respectable people may not say moms and dads matter, but they will still be able to say "two parents are better than one" (and why is it then, that three parents aren't better than two?) or "kids need love and stability." This latter of course is precisely what family advocates have been saying for 20 years: its not marriage or family structure that matters, it is only love, money or maybe stability. This is where the conservative case for SSM melds seamlessly into the liberal case against marriage. And people saying it don't know enough about the marriage debate to even notice!
More "tk" as the copy editors say. . . .