(Warning: this post concerns Californian citizens.)
I have been standing out of US politics for now, but I think this one is not a political issue but more a moral one.
Prop 8 is a proposition that wants to define marriage only between a man and a woman. It obviously excludes same-sex people to get married, and it also reverts the right that same-sex people in California were able to enjoy. It's an obvious moral regression that must be fought.
A YES vote for Prop 8 is a vote for the middle age intolerance. It's an insult to a large minority in this state as well as in the world, which parts of it recognize same-sex marriage.
In my country same-sex people are able to get married since 2003 and so far all churches are still there and are practicing religious weddings as defined in their writings. There is a huge difference between a civil marriage and a religious marriage, only the civil marriage being official recognized.