Hmm, interesting thought-game. I bet a lot of the more decent religious folks would be depressed for a little bit, ask themselves "What was it all for?" etc., listen to emo music, and then in a short time look at the world around, think, "This is still a pretty cool place, and I still don't like to see other people hurting and want things to be fair. Well, God, if this is all there is, maybe I should start working to make things better in THIS life since there's no other life to fix things in."

The selfish or psychopathic were that way with or without religion and will probably act much the same, just without having quite the veil to hide behind. You might get a few who agitate for Nietzchean-style anarchy and nihilism, but all the decent folks would rise up and say, "That doesn't sound like a world worth living in."

And

In the mean time, we need to develop a language for ethics and even "spiritual" experience which is founded in rational and humanistic terms, rather than ancient (and barbaric) superstitions.

Definitely agree with that. I think all of us need to keep speaking out and keep trampling down the lie that the world and people aren't good without God. Start enough memes, and they'll have to add up to something. I think the reason that atheism is off-putting to many people is that they buy into the dualistic stereotype that meaning and significance and morals all fall on the "God" side of the scale, and only us saying the opposite over and over again is going to change minds.