Autodidact
Intentionally Blank
Okay, I'm going to hate myself for responding to this thread.
First off, it wasn't an either/or kind of decisison. The LDS Church contributes enormous amount amounts of money, goods and services to people throughout the world, regardless of their religious beliefs. Per capita, it almost certainly exceeds that of any other church in the world. I believe the LDS Church hierarchy sees Proposition 8 as a moral issue, and sees itself as compelled to support the standard of morality it believes to be mandated by God. (Note: You asked about the Church hierarchy. My answer was directed to that question specifically.)
And apparently believes that it is their business to impose their peculiar "morality" on the rest of us, thereby setting themselves in opposition to basic American values.