dangerous idea: The Moral Argument that Christians don't use, but atheists always rebut

Dr Victor Reppert has posted a very interesting posting posing the following question.

Yet, when I hear atheists talking about moral arguments, they always assume that the advocate of the moral argument is saying that we have to believe in God to lead moral lives, (and indignantly argue that we don't have to believe in God to lead moral lives) in spite of the fact that Christian advocates of moral arguments, at least the ones I am familiar with NEVER say that. 
Why?

I agree with Dr Reppert. I have not ever heard a Christian scholar or apologist argue that unbelievers have to recognize God in order to have a moral code. The argument is that without God, you don't have a foundation for that moral guide any better or binding on everyone. It doesn't matter how often you say that the Bible does not say that godless people do not have morals. The Christian position is that morality is flawed and tainted by sin. So what about Dr Reppert's question. I think atheists default to the strawman position because they cannot give a satisfactory rebuttal to the moral argument for the existence of God and they are too proud to admit their failure.

dangerous idea: The Moral Argument that Christians don't use, but atheists always rebut