In this interview with Kenan Malik (a "scientific author," i.e. a psychology/biology guy who dabbles in philosophical issues) uses the Euthyphro to argue that presenting religion as the guardian of moral values "diminishing the importance of human agency in the creation of a moral framework." His enemy is "false certainty" in ethics, whether because you think that basic moral precepts are given by God and beyond question or that science yields up moral truths (note that since scientific findings are by their nature defeasible, I don't think this description is apt).
In describing Leibniz's view (which agrees with Plato's), Malik makes the same jump from the metaphysical to the epistemological that Matt criticized me for in our discussion (the bolding is mine):
Or, as Leibniz asked at the beginning of the 18th century, if it is the case that whatever God thinks, wants or does is good by definition, then “what cause could one have to praise him for what he does if in doing something quite different he would have done equally well?” If, on the other hand, God recognises what is good and promotes it because of its inherent goodness, then goodness must exist independently of God. But God is no longer the source of that goodness, nor do we need to look to God to discover that which is good.
Now, that point didn't slow down our discussion much, even though Matt pointed out that you could conceive a coherent view by which "the good" is metaphysically distinct from God yet God is the only one who knows it adequately, so we still have to look to scripture or whatnot to get it. I don't know that such a view would be very attractive to any party. Certainly if you see God's creation as part of his revelation to us (general revelation as opposed to the special revelation of scripture), then at least the gist of such an important topic for us to know about should be discernible from nature itself: we're given such gifts as pain and pleasure and moral sentiments and all that. This is why, for Adam Smith, analysis of the human condition leads us to figure out what God commanded, even if mentioning God, for Smith, might turn out on closer examination to be an afterthought to patch up his sketchily conceived metaphysics of morals and to cover himself politically. The important point for him is the epistemological, and I don't see much evidence that he cares about the metaphysics.
As someone sympathetic to phenomenology, I generally share Smith's indifference: what's important for action is how we can know moral truths, and in this way I can compare Plato's method (self-questioning, trying to tear oneself away from the concrete to come up with coherent underlying principles) to the moral sense theorists' (also self-questioning, taking ones moral sentiments as the raw data but reflecting on them to come up with a coherent underpinning that will resolve, for example, apparent differences in the sentiments of those in different cultures) and see quite a bit of similarity despite their differences on the metaphysical matters. I was inspired by Matt, though, to better consider the metaphysical question, and I don't buy Malik's formulation that accepting Plato's argument that God's preferences are non-arbitrary means that there's a metaphysical divide between God on the one hand a preexistent-to-God "good" on the other hand. That kind of metaphysics to me involves positing two different, near-equally bewildering entities: it seems much worse to me than Plato's actual metaphysics of the form of the good being supreme and then there being some divine beings who are neither omnipotent nor omniscient, and certainly less easy to grasp than the Catholic conception of God I've attributed to Swinburne.
So what's the alternative? If, like Swinburne (and Leibniz), you accept Plato's argument, then your metaphysics becomes fuzzy: God is in some way responsible for morality, and the laws of logic for that matter, because God is the ultimate ground of everything, but yet we can make a conceptual distinction between the actions/attitudes of God as a personal will on the one hand and His nature as the ultimate ground of everything on the other. If you want to say God has attitudes at all (which is inherent in having a personal conception of God and not Spinoza's), then you have to say that his attitudes (part of God) are caused by his nature (another part of God), which means that, contra Swinburne, God is not simple after all, but has parts causing other parts. This seems like it's skirting the edge of to some form of polytheism, but Catholics like Swinburne are certainly no stranger to having to explain away things like that, what with the trinity and all.
I've certainly not read enough Swinburne to know how he handles this exactly, but I can imaginatively construct one: Drop the talk of God's nature providing the grounding of morality (and logic), but insist that nothing else provides this grounding either. Unlike a contingent being of the properties of a contingent being (such as the scientific laws that capture in general how contingent beings behave), a necessary law doesn't require any grounding. For example, that there is necessary being itself (God) doesn't need any further explanation, and the laws of logic and basic facts about morality are just necessary in that way.
All of this strikes me as bizarre and unsatisfying, but I'm going to steel myself in 2012 for following Matt's example and taking these metaphysical issues seriously insofar as doing so is necessary to understand that strain in the history of philosophy.