Prop 8 wasn't the Mormons' first time to the hate dance. They've been bankrolling anti-gay legislation for at least two decades. Here is one Mormon's story about how they helped push DOMA in the state of Nebraska.
I lived in Nebraska when a petition drive was held there to get DOMA on the ballot. At church we were not even asked if we wanted to gather signatures. We were handed packets (which I did not take) and several hours of our usual meetings were taken up with our bishop and stake president rallying the troops, so to speak – even sending people out on a Sunday gather signatures at the College World Series. I didn’t speak out against it. I just murmured with my like-minded friends about our disgust over the church getting involved. Hell, damn near running the whole thing. And happy, oh so happy, to join forces with evangelicals who agree with Mormons on nothing other than the so-called moral decline of society.