The only tenet of which should be, “Two people who love each other should be allowed to marry.” Maybe two tenets, the other being, “Be excellent to one another,” which has its plusses, too.
At which point, the opportunity to have same-sex marriages becomes one of religious freedom. To restrict such marriages becomes a first-amendment issue, which carries more weight than equal protection, apparently.
Of course, I would hope that many heterosexual couples would also want to get married in the First Church of Fabulousness–it being fabulous, see–but, you know, they, too, could exercise their right to choice.