Blame The Catholics Too

According to the SF Chronicle, the Mormon Church didn't join into the marriage equality battle until the Catholic Archbishop of San Francisco invited them.

Months before the first ads would run on Proposition 8, San Francisco Catholic Archbishop George Niederauer reached out to a group he knew well, Mormons. Niederauer had made critical inroads into improving Catholic-Mormon relations while he was Bishop of Salt Lake City for 11 years. And now he asked them for help on Prop. 8, the ballot measure that sought to ban same-sex marriages in California. The June letter from Niederauer drew in the Church of Jesus Christ of Latter-day Saints and proved to be a critical move in building a multi-religious coalition - the backbone of the fundraising, organizing and voting support for the successful ballot measure. By bringing together Mormons and Catholics, Niederauer would align the two most powerful religious institutions in the Prop. 8 battle.

The same article notes that a last-minute shift among Catholic voters provided enough of a margin to pass Prop 8.

The last Field Poll, conducted a week before the election, showed that weekly churchgoers increased their support in the final week from 72 percent to 84 percent. Catholic support increased from 44 percent to 64 percent - a jump that accounted for 6 percent of the total California electorate and equivalent to the state's entire African American population combined. The shift in Catholics alone more than accounted for Prop. 8's 5 percent margin of victory.