Non-Human Moral Authority

Adam, of Daylight Atheism fame, argues that since there are no non-human sources of ethics, we must act according to some human-created ethic or other.  Here's the quote he's critiquing, from Peter Hitchens (the late Christopher Hitchens' brother):

"For a moral code to be effective, it must be attributed to, and vested in, a nonhuman source. It must be beyond the power of humanity to change it to suit itself."

And here's Adam's response:

The fatal flaw in this position is that, contrary to your confident presumption, there is no non-human moral authority. Every religious book is written, edited, and printed by humans. All moral opinions, interpretations, and proclamations are human opinions. If there were a huge, glowing set of tablets with commandments engraved on them that descended from the sky accompanied by angels blowing trumpets, and the choice was between following those or making up moral laws on our own, we'd be having a very different debate; but there is no such thing.

I don't know precisely what Hitchens was arguing here, but from the quote itself it appears that Adam's missing the point.  Vested in a non-human source doesn't mean made up by a non-human source.  What does it mean?  Well, we're told: an ethics that's vested in a non-human source is 'beyond the power of humanity to change it to suit itself'.  Adam thinks the only kind of ethics that falls into this category is divinely-dispensed commandments - but what about, for example, Kant? 

Kantian ethics is based on respect for the rational nature of others, and Kant certainly believed that it could be derived using pure logic.  Rationality could easily be conceived of as a non-human source, beyond the power of humanity to change. Sure, it's a made-up moral law, but it fulfils the criteria that Hitchens set for an effective moral code.  Adam's post could have been quite interesting - can non-theistic philosophy provide an effective non-human basis for morality, and, if so, how - but instead it's a thousand or so words of straw.