Earlier I posed the question of whether a naturalist could use the argument from evil, if that naturalist was not a moral realist. Some commentators have pointed out that the argument could be advanced by someone who rejected moral realism used moral realism as a reductio ad absurdum argument against theism.
Let's look at the argument from evil again.
1) Gratuitous evils probably exist.
(2) Gratuitous evils are incompatible with the God of theism (omnipotent, omniscient, all-good).
(3) Therefore, the God of theism probably does not exist.
If the defender of the argument from evil is unwilling to argue that 2 is true, she must at least argue that 2 is entailed by theism. In other words the defender of the reductio must do more than show that theism entails moral realism. I am personally inclined to think that that is true. A theist who believes that God gives commandments cannot maintain that one person's opinion is just as good as another's where conduct is concerned, if one of the persons is God.
But all you need to be a moral realist is to hold that there are at least some moral truths. It's perfectly possible to be a moral realist and to deny 2. An atheist using this version of the problem of evil must show that someone who is a theist and a moral realist but denies to is contradicting herself. That's a tall order.