But don't those you're trying to persuade think that it precisely isn't the church's choice -- it's to do with how God made the world? They don't see themselves as defining marriage, but as recognising something present in the universe's blueprint. So you can't hope to persuade them by saying they can redefine marriage; you'd have to either persuade them that they are wrong about what 'marriage' means, or that there is no such thing written into the universe.

S.