I agree, but so far as I can see the strongest arguments against moral realism actually work just as well if there is a god as if there isn't -- unless you cheat by defining your god in a way that presupposes moral realism. That's a common move, of course, and I'm sure it's not generally intended as any kind of cheating, but none of that makes the argument "I have defined 'God' in a way that presupposes moral realism. It turns out that there aren't good non-theistic arguments for moral realism, but if you define 'God' my way then it's easy to deduce moral realism from his existence. Since we all know that moral realism is correct, this is evidence for God." a good argument.