Carrier spends a good 30 pages outlining his moral theory, but it essentially boils down to enlightened self-interest. This perhaps comes out most clearly in just two pages (323-324) where he has to argue that secret violations of moral laws will not lead to happiness.
Think about this in the context of Carrier's appearance on The God Who Wasn't There
Flemming: Let me give you a scenario. You're dead... You find yourself in Hell. You're being roasted on a pit, and every hour on the hour your have to suck Satan's greasy cock... don't you wish you would have believed? It would have been so easy just to believe.This overlooks one possibility: that God would work some miracle to prevent the people in heaven from feeling bad about the people in Hell. Some Christians have seriously proposed such a solution. But I doubt Carrier would be enthusiastic about such a deal.
Carrier: Well, no, because it wouldn't really be any better. If I had to sit in heaven forever, knowing that there are these people, millions and millions and probably billions of people, suffering these eternal horrible torments, and there was nothing I could do for them, that to me would be hell.
This very brief analysis, I think, is sufficient to show that Carrier's actual moral principles are higher than his philosophy. The problem is obvious to the point of being impossible to miss.
Finishing this critique, I can't help but feel that with Sense and Goodness, carrier inserted himslef into the wrong field. He's a good historian--has produced fascinating stuff, including some of the best criticisms of historical apologetics out there, helped get me interested in history--he just isn't a very good philosopher.
I suppose this post wouldn't be complete without an explanation of my own views on meta-ethics. I'll be upfront: I don't know. I just think that Carrier's view is such an obvious nonstarter that it should be off our list of candidates.
One proposal that's been thrown out (for example, by Gene Witmer) is atheistic Platonism. It strikes me as having an edge on theistic theories in terms of parsimony: It's "Metaphysical standard of morality" vs. "metaphysical standard of morality that is an omnipotent, omniscient person." Being an omnipotent, omniscient person has nothing to do with morality as far as I can tell. Some theists would argue that an omnipotent being would be needed to enforce moral laws, but then we're back to enlightened self interest and the problems that come with it.
Still, I'm not ready to embrace Platonism. It still suffers from one of the major problems with theistic theories: it pushes the problem back a step without ever really answering it. To the theist, one cannot help but ask "but why must we follow God's commands?" To the Plantonist, one cannot help but ask "why must we act in accordance with these abstract entities" and "where did they come from?" Oh well. This is why the field of philosophy exists.