On the traditional DCT, God determines right and wrong by issuing commands. Moreover, from a moral standpoint, these commands have to be arbitrary. (If they weren’t — if there were some moral reason why God commands one thing rather than another — then there would be something other than God’s commands making things right or wrong.) But this arbitrariness means that, morally speaking, God can command anything he wants. There are no moral rules preventing him from doing so. It is therefore in principle possible for God to permit anything. It follows that on the traditional DCT, anything might be permitted.
Nor is this problem entirely solved by modified DCT. Modified theorists say that God’s nature is such that he can only command those things that are compatible with his nature. Thus, they may argue that God is by nature a loving being — and therefore that we can say that cruelty, for example, will never be permitted.
However, if the most fundamental principle of modified DCT is that it is God’s nature that determines what is good, then it follows that that is the case even if theists are wrong about what that nature is. But in that case, they must admit that it is possible that they are wrong about what might be permitted. In other words, if what makes something right is that it is a command that follows from God’s nature, and theists might be mistaken about that nature, then they cannot rule out anything being permitted.
At this point, some theists might of course reply that they cannot be wrong about God's nature. And yet, these are the same people who on other occasions say that no one can truly understand God's ways. Or who, when something bad happens, say that God must have had his reasons — reasons which he obviously has kept from us. But then God may also have a reason to hide his true nature from us.
It appears that it is the DCT, then, and not atheism, that creates this kind of problem for morality.
[Originally published at Debunking Christianity]