As a staunch supporter of civil rights for all, I will vote no on California proposition 8, and hope you'll do the same. I agree that this is a vote for loving gay families, and a pro-family stance which simply recognizes that not all families are of exactly the same configuration.
But it is also a matter of fairness under the law. Civil marriage is a civil contract. Proponents say that without Prop 8, the court has created a "protected class" and that allegedly makes all sorts of things mandatory under California law (teaching gay marriage in schools, for example). However, if Prop 8 passes, I say it will create a "rejected class" of people who are excluded from an important section of civil law. I believe that doing this undermines that section of civil law, and sets a precedent for further attacks on the Equal Protection clause of the U.S. Constitution. It's not gay marriage, but that kind of "separate but equal" approach to civil unions vs. marriages, that serves to undermine the legitimacy of civil marriage.
Additionally, the freedom of religion argument in favor of Prop 8 is utterly bogus. The California courts ruling should not compel churches to perform gay marriage ceremonies against their beliefs, rather only require the state to recognize same-sex civil marriage as valid. On the other hand, Prop 8 will impinge upon the religious freedom of churches that do wish to allow same-sex couples to marry under their auspices. It is actually Prop 8 that is in opposition to religious freedom.