All other things being equal, which of course is never the case, isn't a kid living with two parents, one male, and one female, probably the most ideal for the kid - you know gender role models and so forth? As others have stated, just because something is best, does not mean that some law should mandate it (among other things, as I said, all other things are really never equal). The elusive theoretical perfect can be the enemy of the practical good.
Not really. My parents had a very ugly marriage. My quality of life improved immensly when they got divorced. And I don't think I'm alone in saying I'm tired of santimonious Republican politicians telling me what my family is supposed to look like. For a party that claims to be for "small gov't" they're strangely obsessive about what people do in their own homes on their own time.
The phrase "all other things being equal" is just so highly useful isn't it?