Benedict describes as "presumptuous and false," the idea that "[s]ince there is no God to create justice ... man himself is now called to establish justice." "It is no accident," he said, "that this idea has led to the greatest forms of cruelty and violations of justice .... A world which has to create its own justice is a world without hope." No. 42. Justice will be whatever man decrees. Thus Kelsen [some legal positivst] said that Auschwitz and other Nazi exterminations were "valid law." In accord with his "philosophical relativism," he could not reasonably criticize them as unjust.
(Ellipses and brackets in Rice.)
That's right: Plato's Euthyphro caused Auschwitz. The fact that it took a couple millennia just shows that the Catholic Church is the only thing standing between a humanist ethics and genocide.
Frankly, I don't get it. Ratzinger was an academic theologian for 26 years. Presumably at some point during that time he encountered at least a few ethicists and moral philosophers who (a) are not divine command theorists and (b) also not anything-goes moral relativists. Now maybe he doesn't think that their positions are consistent or whatever. That's fine. But he should at least recognise the need for an argument that (a) implies (b). You can't have a reductio ad absurdum without the reductio.
Bonus egregious academic dereliction: Charles Rice, emeritus professor of law, displaying his complete lack of understanding of the difference between logical positivist ethics (which is an anything-goes moral relativism) and legal positivism (which, as I understand things, just distinguishes legality from justice).