Why treat us differently?

After my response to a comment on a previous post, about how different relationships can be treated differently comes this post from Andrew Sullivan's blog on the same basic point:

"Think of the diversity of lived experience that now exists within this civil institution in America. You have strict Catholic families with no divorce, no contraception and lots of kids in a very traditional fashion; you have childless yuppie couples, living in different cities; you have arranged marriages among some immigrant families; you have a newly married couple in their seventies; you have Larry King on his seventh and Dennis Prager on his third; you have Britney Spears' 55 hour special; you have teenage elopers and middle-aged divorcees; you have a middle class evangelical couple with three young kids and two working parents; you have George and Barbara Bush and Demi Moore and Ashton Kutcher; you have open marriages which amount to sexual arrangements; and Mormon marriages whose sexual monogamy will continue physically after death.

Are people really saying that a lesbian couple of several decades or a newly married couple like me and Aaron fall outside the cultural range of these experiences? Civil marriage is already so broad in its inclusion of social types and practices that including gay couples will make virtually no difference at all. And this is the genius of civil marriage: it's a unifying, not balkanizing, civic institution. To argue that including gay couples destroys the institution is absurd."