Traditional marriage is one man with multiple wives, multiple concubines, wives conquered in war and wives acquired in levirate marriage, possibly including girls under the age of ten, but definitely not including anyone of a different ethnic group, in an arranged marriage with disposition of property as its purpose. That seems very different from “one man, one woman,” does it not?
Of course, it’s easy to say that marriage as an institution evolves—but then, if we admit that, we have to admit that sanctioning loving, same-sex unions is just another step in that evolution. Perhaps this is why the Tony Perkinses of the world simply ignore the Bible when it doesn’t suit their purposes, instead preferring to make pseudo-scientific (and wholly unsupported) claims about what’s best for children and society. The Bible’s truths are just too inconvenient.