NPR:

Attorney Charles Cooper [argued] that same-sex couples can be treated differently when it comes to marriage without running afoul of the Constitution because "sexual relationships between men and women naturally produce children." "Society has no particular interest in a platonic relationship between a man and a woman no matter how close it might be, or emotional relationships between other people as well, but when the relationship becomes a sexual one, society has a considerable interest in that," Cooper said. "Its vital interests are actually threatened by the possibility of an unintentional and unwanted pregnancy."

Um...

If the state's vital interests are threatened—actually threatened—when unmarried heterosexuals experience an "unintentional and unwanted pregnancy," why isn't it illegal for unmarried heterosexuals to get pregnant? Why aren't unmarried heterosexuals who get pregnant legally compelled to marry? Why aren't there penalties—steep fines, long prison terms, court supervision—for unmarried heterosexuals who get pregnant and refuse to marry?

But wait! The lawyer defending Prop 8 in court yesterday didn't identify an unintentional pregnancy as a threat—an actual threat—to vital state interests, he said the mere possibility of an unintentional pregnancy represents a threat. So it really should be illegal for unmarried heterosexuals to have sex at all.

Denying marriage to same-sex couples does nothing to diminish the threat—the actually threatening actual threats!—of unintentional and unwanted pregnancies among straights. We don't need to ban gay marriage to deal with this threat. We need to ban straight premarital sex.