Marriages mean weddings. Weddings mean parties, with cake! More marriages mean more weddings. More weddings mean more parties, with more cake! Allowing gay marriage means MORE CAKE and MORE PARTIES.
(Well, I’ve seen people present Christian arguments in support of gay marriage, Conservative ones, Liberal ones, Social Justice ones… But I know my country. Any argument that does not involve the hope that a drunken bridesmaid will have a wardrobe malfunction is not persuasive to our people.)