In the second comment to this post at Thinking Christian, Jospeh A. writes:

On the flipside, I can say that I often come across atheists who tend to display a systematic disconnect with what their beliefs naturally demand, or at least lead to. … Watch how often you’ll come across atheists who talk about good and evil, or even right and wrong with regards to morals as if there were really an objective, ultimate standard in play. 

I’m willing to admit that there are atheists who display a systematic disconnect with what their beliefs naturally demand. But I don’t think the existence of atheists who believe in objective morality is necessarily a good example of atheists having a disconnect. I am an atheist, and I believe in objective morality, and I don’t think I’m being incoherent in doing so.

This gets at a standard Philosophy 101 topic, the Euthyphro Dilemma. Is killing an innocent person wrong because God says that it’s wrong, or does God say that killing an innocent person is wrong because it really is objectively wrong? Some people, like Joseph A., believe that God determines what is objectively morally wrong or right. If God says that it’s morally permissible to rape children, then it’s morally permissible. In contrast, I say that, even if God exists, the objective moral standards aren’t set by God. If God were to say that raping children is morally permissible, that wouldn’t make it morally permissible; it would just mean that God is incorrect. 

Most theists think that it’s impossible for God to be incorrect, so in practice God would always prescribe the correct moral view. But it doesn’t follow from the fact that God always prescribes the correct moral view that God is the source of morality. 

Of course, I haven’t conclusively argued for this, and I don’t have such a conclusive argument — nor, in my opinion, does the other side. This is one reason that it’s such an enduring philosophical dilemma. I raise the issue here mainly because I don’t want theists to just assume that all atheists think, or have to think, that there’s no objective morality.