Indeed, whenever I see supernaturalists peddling this piece of apologetic nonsense, the end result usually translates into:

Objective Morality = Magic Man Says So

which is about as "objective" as the palatability of Marmite.

Quite simply, anyone who actually bothers to study ethics as a discipline in its own right, quickly learns that all the ethical systems generated by humans (including those purportedly arising from a mythological magic man) depend upon choices of axioms. Whether your preferred ethical system of choice is deontological, consequential or utilitarian, each of these arises from a choice of axioms.

Perhaps the most duplicitous expression of the requisite apologetics, comes from the "divine command theory" brigade, who effectively assert that "Magic Man says so" is an imperative demanding unquestioning obedience, even when Magic Man orders two entirely contradictory actions in quick succession. Which is a venomously dangerous assertion, not least because the only source of purported "data" on this matter, comes from those who assert that they have a special hot line to said magic man. Susan B. Anthony's aphorism comes into play at this point, and frequently in a manner that brings the malignancy of the "divine command" assertion into sharp relief.

One of the most notorious exponents of "divine command theory" is William Lane Craig, whose apologia for genocide on these grounds is particularly nauseating to observe. Indeed, at least one properly tenured philosopher of religion regards Craig's position as flawed, even dangerous. The full citation for that paper, in the interests of honest discourse, is:

God And The Ontological Foundation Of Morality by Wes Morriston, Religious Studies, Volume 48, Issue 1, March 2012 , pp. 15-34 DOI: 10.1017/S0034412510000740 [Full paper is a free download from the journal via this link]

Morriston opens his paper with:

I have three principal aims in this article. The first is to interpret and clarify Craig’s account of the ontological foundation of morality.[2] The second is to press an important objection to that account. The third is to expose the weakness of Craig’s arguments for saying that in a Godless world morality would be groundless and illusory. If these arguments are as weak as I believe them to be, then Craig has yet to give anyone who is not already a theist a reason to adopt his account of the foundations of morality. And if my objection to Craig’s account of the relationship between God and morality holds up, then theists and non-theists alike have a strong reason to reject it.

As an example of critique of the requisite assertions, Morriston presents the following objection that has been presented by past authors (emphases mine):

Either God has good reasons for his commands or he does not. If he does, then those reasons (and not God’s commands) are the ultimate ground of moral obligation. If he does not have good reasons, then his commands are completely arbitrary and may be disregarded. Either way, the divine command theory is false.

However, in order to deal with Craig's well-known elisions and shell games, Morriston goes deeper, as the paper reveals to anyone who reads it. At the end, a nice stiletto thrust is provided by the following:

The first is simply to deny that duties must be constituted by commands in order to have imperative force. There are, after all, lots of normative laws that do not require a lawmaker. If, for example, you know that two propositions are inconsistent with one another, and you also know that one of them is true, then you should not accept the other.[25] Nobody thinks we need a ‘divine command’ to back up this rule. I see no reason why it should be different for moral rules. If this is right, then the way is open for the non-theist to say that basic moral duties are fundamental moral facts and (like moral values) require no further foundation or ground.

But suppose something further is desired. Here is another option. It is a variant of the ideal spectator theory. Even an atheist might consistently identify duties with commands that would be given by a perfect being. That might not settle every question we’d like have settled; but it would certainly make it a duty not to kill or steal or practise cruelty. Interestingly, such an account fits nicely with Craig’s claim that God’s commands ‘flow necessarily from’ his perfect moral nature. Even by his lights, there must be a fact of the matter about what a being possessing a perfect moral nature would command if there were such a being. Once again, it turns out that the actual existence of God makes no difference to the ontological foundation of morality.

In conclusion, then, neither of Craig’s two theses holds up. T1 may be true, but only in a trivial way. For all we’ve been shown, morality has whatever foundation it requires whether or not God exists – in which case, of course, it has whatever foundation it requires if God does exist. On the other hand, T2 (and, of course, itssubjunctive sibling) appears to be straightforwardly false. A Godless universe could contain loving and just persons, and if it did they would still be morally good. It might contain acts of cruelty, and if it did those acts would still be morally wrong. Neither moral value nor moral duty need be illusory in a Godless universe.[26]

I suspect several here will enjoy reading that paper in full.