By any measure of rationality, the likelihood of God's existing is vanishingly small.

Boy, you are sitting on a can of worms and trying to pretend it's a toilet seat with that one. If by "God" you mean the overmuscled pater noster flying through the universe with a bad attitude, I am inclined to believe you. But if you (as you seem to do) embrace in that word all the meanings it has been attached to, I would say you failed to tag first base.