Cruel Logic

Found this great video by Brian Godawa. What happens when a atheist who believes morality is evolved or some kind of social contract is FORCED to defend their position? While the video is admittedly a bit twisted, the point is clear... "Ideas have consequences." To deny God, is to deny the only possible basis for objective morality. Some people are fine with objecting to objective morality in theory, but they will ALWAYS sneak it in through the back door. Even if their theory states that morality evolved to help the species survive so that we care for our genes, they sneak in the moral obligation that we ought to care for our genes. But that is the point... what is the basis for the ought? If it is evolved then it may be helpful, but it can never be obligatory.