It also relies on the claim that this god's moral rules should be normative. That is, we should actually believe that these rules are moral and that we should actually desire them. That is what we usually mean by morality as opposed to doing something just because someone bigger than me tells me to do it.
But then, I find the meta-ethical question why should we feel these rules are right to be interesting as well.
To count as an atheist, one needn't claim to have proof that there are no gods. One only needs to believe that the evidence on the god question is in a similar state to the evidence on the werewolf question. -- John McCarthy