I no longer live in California. If Prop 8 passes, I likely will never go back. Why should I support a state whose voters legalized discrimination?
If it passes, and it looks like it may, then likely it should be challenged on the basis that it violates the US Constitution, specifically the First and 14th Amendments. The First Amendment argument is subtle, nuanced, and utterly correct: Prop 8 DOES impose unambiguously 'sectarian' prohibitions on all citizens regardless of their religious (or irreligious) affiliations.
But Murkins, even the ones wearing the black robes of jusice, do not DO "Nuance." So the best approach is via the 14th Amendment. Gay marriage is a slamma-jamma ginormous DUNK under the 14th Amendment, as long as states continue to ratify marriages between hetero couples...These are very good ads, btw...
Note: I am not a lawyer, but have played one in the movies...AND have stayed at a Holiday Inn.