And there is no basis for saying that I can't just shoot a man down in cold blood or abort a baby or strangle my wife in her sleep.
Anyone who says otherwise is lying.
I believe a better way to phrase it is that without a Supreme Being holding us accountable to written moral standards, we are free to make up our own moral standards on a minute to minute basis.
For example, an atheist can live a perfectly good and moral life. Then one day they see $100 left on the clerks desk at the store and nobody is looking.
A religious person may take it but likely will not.
An atheist may take it and can easily justify their action without fear of ramifications.