Not trying to pick on D. Glen Whitman, but in our exchanges below he has made a point that others often do:
And while God has allegedly given us an instruction manual with the moral truths written down, there is more than one such manual, and their contents are often ambiguous and inconsistent. That means that we have no choice but to use reason to try to figure out the best moral rules.
As always, my point here isn't to change minds; obviously that's not going to happen. But I get the sense that there are many atheist readers of this blog who would think Glen hit the nail on the head here, and only moronic Christians could contort their minds and fail to see how crushing this point is.
On the contrary, it's no more crushing to the Bible-thumper than the following analogous argument is to Glen:
Rationalists allegedly tell us that reason can allow us to discover moral truths. Problem is, rationalists don't agree with each other. Even if we narrow the category down to atheist libertarians who love Rothbardian legal theory, they don't all agree on something as important as abortion. This just shows how vague and unhelpful reason alone is, if it isn't supplemented with our intuitive conscience that (I would argue) comes from our divine background. (In contrast, Hayek would say it comes from evolution. But he too would deny that reason alone gives us morality.)