In her post, Is Humanism Arrogant?, Terri Murray offers an undergraduate level textbook recitation of divine command theory, attributing the position to Christian "theocrats", theologians and otherwise, who engage in a worldview analysis that draws the conclusion that humanist ethical theory represents arrogance because it ultimately lacks any epistemic foundation. Oh yeah, she never explained the reasoning of these "theocrats."
Terri fails in this post, not because she created a strawman--yes, there is much more to Christian ethics than divine command theory--not because she doesn't answer the "theocrat" according to the strawman she set up in the first place, but because she never actually offers an explanation for how humanists "understand" ethics. Frankly, I'm not even sure what "understand" means, unless she is referring to how they ground ethics. If this is the case, she might have better expressed it as an accounting of ethics. So how do humanists account for ethics?
Every worldview has a self-sufficient. In biblical Christianity, the self-sufficient is the God of Scripture. In humanism, the self-sufficient is man who, through the use of reason, locates right and wrong, the ethical and unethical. But in the history of humanity, man has proven that the use of reason never yields the same conclusions among all men. Reason fails. Science is not ethics, science is a descriptive discipline, ethics is a prescriptive discipline. Science can never speak for ethics, it can only offer choices to ethics. Humanism fails the test for objective ethics, and with relativism as that which remains, humanist ethics can never speak for everyone, nor would it ever try to. The fact remains, humanism simply cannot account for right and wrong, because humanism cannot escape relativism. And that's why the charge of arrogance hovers over humanist ethics.