Marriage as a religious institution

The Right frequently claims (and occasionally gets a candidate, like Obama to do the same) that marriage is a religious institution. So Maryland state senator Jamie Raskin said, fine, we'll leave marriage to the church and change all the marriage laws to refer to "domestic partnerships" which would be available to both straights and gays. The Right predictably called a foul, saying "They’re creating a situation for one special interest group that basically diminishes the value of marriage for everyone else." But doesn't that make marriage a "special right" for straights? Perhaps the Right should jump on the offer to forestall the time that government decides to regulate baptism and communion.