I'm still hoping to get winstoninabox to answer the question posed by Dostoevsky's Grand Inquisitor.
In the meantime, here is a quote from Christopher Isherwood, in 'The Condor and the Cows', that asks a similar question.
"As for the militant atheists of the Left Wing, their smug stupidity appalls me. It is all very well to brand certain cults and legends as superstitious, and to attack the political crimes of the historic sects, but have they never stopped to ask themselves what religion itself is for? How in the world do they imagine they can make their free democratic community function when they have removed the whole spiritual basis of consent? Don't they know anything about human nature? Do they really think that justice and public ethics can operate in a vacuum? No- they are too busy getting on with their revolution. They take it for granted, with an optimism that is mystical in the worst sense of the word, that the fundamental problem will somehow solve itself."