The Prop 8's lawyer's answer appeared to suggest that a person 55 years old can in fact bear children (regardless of age, regardless of sex, apparently), although Justice Kagan, taking pity, gently disabused him of this notion. When one is defending an irrational prejudice, this is the sort of blind alley you wind up wandering down. You are met at every turn with the utterly stupid implications of what you are advocating.
The best questions were from Justice Kennedy, who could not see why the ban on same-sex marriages was legally distinguishable from the unconstitutional ban on interracial marriages, which the Supreme Court has already disposed of.
Personally, I think the answer to all of these questions is pretty obvious, but hidden in plain sight: get rid of all legal implications and complications of the marital state. Allow anyone or anything to marry any other person or thing, in any number, that he, she or it chooses to marry. If churches want to bless the sacrament of marriage with their rituals, let them. If a guy on your bowling team wants to perform the marriage ceremony for you and your girlfriend on the basis of some incantation he downloaded from the Internet, that should fly. If you want to marry your dog, or turtle (to handle Rick Santorum's gotcha reductio ad absurdum), then you should be allowed to marry your dog, your turtle, or to enter into polygamy with both of them. As long as you're sincere. I insist on sincerity.
As part of the same liberalization, all laws should be restated and restructured to get rid of all references to the marital state. The condition of being married should have no effect on taxation or other legal rights (no filing of "joint returns," no "marital deductions" on estate tax forms, no "survivor's rights" to Social Security, none of this bullshit). If an adult wants to visit you in the hospital, and it's okay with the patient (either through volition or Advanced Directive in the event of incompetence), then the hospital ought to let the person visit. Divorce law, including alimony, property rights and the rest of the traps and snares should be eliminated altogether. Instead of divorce we will have "breaking up," with both parties (male, female, reptile) then left to their own devices.
I am all for marriage equality. It's a bad idea to enshrine prejudice with legal proscription, as was done in California with Proposition 8. California passed, in essence, a Jim Crow law in the (Mormon) guise of "protecting the family." It was a huge step backward, but it will not last. Either the Supreme Court will overturn it (if the white conservative bigots, the African-American Justice Me-Too, and the closet case on the High Court can be overcome), or the people in California will throw it out with a subsequent initiative.
But granting access of gays to marriage (which they deserve, as things stand) leaves in place another prejudice: that against single people or people in relationships not "sanctified" by marriage. We don't see that discrimination so easily because it is the ocean and we are the fish. Like the other prejudices that have given way to modernity in other categories of discrimination, the preference for the absurd institution of marriage will take time to overcome. But it too will pass away in the goodness and fullness of time.