When I started reading your comment, I was about to cite Israel, and then you did. Yes, I don't think we would do very well in the U.S. if marriage were only a religious institution. In Israel, many Jews can't get approval to be married because the rabbis in charge of such things don't recognize certain Jewish denominations.
Originally Posted by Ptichka
What is separate in the U.S., and should be, is that no religious institution can be forced to perform a ceremony that is against its doctrine. Even if gay marriage is legal, no cathedral will be forced to hold a wedding between two men or two women. The government has no power to compel such a thing, just as it cannot now force the Catholic church to recognize a civil divorce and subsequent remarriage, and it can't compel an Orthodox Jewish husband to grant a get (sort of a divorce consent) to a wife petitioning for divorce.