When asked by Chris Wallace where in the Constitution is there a right to same-sex (i.e., gay) "marriage," former Bush Solicitor General and co-lead attorney for the parties who challenged California's Proposition 8 answered with a rhetorical question that it exists in the same place where there is a right to interracial marriage. Of course, no such right is expressly stated in the Constitution, but the Supreme Court has previously determined within the context of state racial segregation laws banning interracial marriage that marriage in general is a fundamental right that is constitutionally protected.
OK, via Ted Olson's comments in the video below, we now know for certain that pro-gay "marriage" advocates are hanging their hats on the premise that same-sex attraction is race. I personally find this ridiculous, but I'd be interested in reading any defense for this position.
A couple of pet peeve house cleaning items: I wish people would stop referring to Proposition 8 as a "ban" on same-sex "marriage." The democratically approved state constitutional amendment simply provides a legally recognized definition. To "ban" something basically means to outlaw it. Proposition 8 outlaws nothing.
I also wish people would stop saying Proposition 8 prevents homosexuals from getting married. Again, it does no such thing. In effect, Proposition 8 limits a legally recognized marriage to 1 male and 1 female. Said male and female may either be heterosexual or homosexual. There is no exclusion from marriage on the basis of sexual orientation. Under Proposition 8, "marriages" between members of the same sex are not legally recognized. Such is true regardless of whether these "marriages" are between couples of the same sex who are homosexual or heterosexual. (Oh, can same-sex couples only be homosexual? Why?).
Update: In his interview with Chris Wallace (the above embedded video was edited by whoever posted it on YouTube), Ted Olson repeated the assertion in Judge Walker's written decision that lawyers defending Prop. 8 said they didn't have to prove or provide evidence of the procreative purpose of marriage. That assertion by Walker is patently false. For Olson to knowingly perpetuate Walker's false assertion really reflects poorly on his character.