Jess - "shouldn't we all just grab a textbook on introductory moral philosophy?"

That would seem ideal. I'd recommend James Rachels' The Elements of Moral Philosophy for a very engaging and easy-to-read introductory text. Though I take it Eliezer is here more interested in meta-ethics than first-order moral inquiry. As always, the Stanford Encyclopedia of Philosophy is a good place to start (then follow up Gibbard and Railton, especially, in the bibliography).

On the other hand, one shouldn't let the perfect be the enemy of good discussion. Better to reinvent the wheel than to go without entirely!