A couple weeks ago a couple Mormons on mission came to my door and I asked them exactly that; they said that yes, the church and its members were against homosexuality. They weren't aware of anything the church itself did for Prop 8, but did admit that various members of the church were probably inspired to donate or work towards the proposition that marriage should be kept between a man and a woman.

I didn't press them on the issue; I'm glad I kept it civil, but I want them to send the message back to wherever it is they report in, that they're hearing this question a lot, and it's making people less receptive.