Internet Christians commonly claim that without "God" there is no morality.
If God commanded people to start eating babies, what would you do?
There are three possible answers:
1) "No, it would still be immoral." That one's easy, and the best answer, and of course it demolishes the idea that God dictates what is moral.
2) "God would never do that, because God is moral." In order for this statement to have any meaning, morality must exist independent of God -- otherwise we could not decide whether God would do a particular thing based on whether or not that thing was moral, because that would be synonymous to asking ourselves whether God would do a particular thing based on whether God would do a particular thing.
3) "Knives out and start the rotesserie!" This, and only this, preserves the idea that morality comes from God, and only from God.
POTW for sure...