Jonathan Rauch compares them. The whole thing is worth a read. Here is part of his conclusion:
I believe that, slowly but surely, family values are renormalizing and will continue to renormalize around later family formation and an ethic which stresses responsible childbearing over abstinence from sexif only because economic and cultural forces are pulling so hard in that direction. At a time when even many young traditionalists (evangelicals, for example) take contraception for granted, are unable to abstain from sex until marriage, and are unwilling to accept shotgun weddings, it is hard to see how the old unity of sex, marriage, and procreation can be sustained. In today’s world, progress has got to lie in the direction of discouraging early family formation and encouraging (and improving) education.
Therefore it is hard to see how limiting marriage to heterosexual couples can continue to make much sense even in Red America. I don’t think excluding gay couples from marriage will do anything to strengthen or restore the old sex/marriage/procreation unity, and I think trying to hold homosexual couples to the old norm while heterosexuals live by the new one will be counterproductive as well as unfair.
(Image: Kate Kuykendall (L) and her wife Tori Kuykendall (R) with their daughter Zadie attend a gay rights rally against the Proposition 8 measure at the El Pueblo de Los Angeles park on March 4, 2009. By Mark Ralston/AFP/Getty Images)