The thing is, Skeptic, that we are not talking about the occasional sociopath, for whom a god, or lack of it, would not make a difference.
You can talk about atheists "borrowing" the Christian sense of morality, but you are not answering the questions of why, if that is the ONLY source, there are societies which still hold similar morals without the Christian background. If you claim that this code is written in their minds/hearts or whatever, then why is it that they often manage to follow it so much better than those raised with a strict belief in the God of the Bible? Surely, even a "false" Christian would have a leg-up on getting at least some of the philosophy right. Yet, over and over we see higher rates of crime, divorce etc, in the Bible Belt.
And if atheists, too, are only "borrowing" the morality, how is it that THEY, in the vast majority, also manage to stay married, out of jail, be involved in charities, and any number of other things in greater percentages than Christians? How is it that those countries which are the most secular continually score highest in quality of life, without their citizens killing each other off, looting and raping to their hearts' content?