A few comments on why it’s a useful discussion:
1. Singer is representative of the modern secular intellectual. Sure, he advocates some highly controversial ethical positions, but his general outlook isn’t fringe. In a sense, he’s only controversial because he’s willing to say openly what he takes to be the logical implications of his worldview. Singer takes for granted the standard naturalistic evolutionary account of human origins. His approach to ethics is a modern, sophisticated version of utilitarianism. He doesn’t have a religious bone in his body, so it would seem, and he doesn’t think there’s the slightest reason to believe in God. I got the impression he could barely conceal his incredulity at Bannister’s views. I suspect he rarely interacts with orthodox Christian intellectuals.
2. Singer trots out the old Euthyphro problem as if it deals a swift death-blow to any divine command theory of ethics, but there’s no evidence that he’s familiar with (or even interested in) the standard responses that have been offered by Christian philosophers. He also thinks the problem of suffering is devastating to any theistic worldview; he can’t begin to understand why an omnipotent, omniscient, omnibenevolent creator would allow the amount and intensity of suffering we find in the world. (Note how much he rests on assumptions about what God would or wouldn’t do. Atheists just can’t help theologizing!) All of this is fairly typical of 21st-century atheist intellectuals: smart and articulate, yet superficial and uninformed in their criticisms of Christian theism.