I don't claim that. "Arbitrary scenarios" is way too wide a class. It's like asking a picture classifier to confidently detect tanks or their absence in arbitrary pictures, even very noisy and confusing ones. (Sorry for the analogy overload!) I only claim that, given the power to rearrange the universe, I would rearrange it into something I would confidently consider "pretty good".
lukeprog gave a list of metaethics questions here:
Most of these questions make no sense to me. I imagine that the moral intuitions in my brain come from a special black box within it, a "morality core" whose outputs I cannot easily change. (Explaining how my "morality core" ended up a certain way is a task for evo psych, not philosophy.) Or I can be more enlightened and adopt Nesov's idea that the "morality core" doesn't exist as a unified device, only as an umbrella name for all the diverse "reasons for action" that my brain can fire. Either perspective can be implemented as a computer program pretty easily, so I don't feel there's any philosophical mystery left over. All we have is factual questions about how people's "morality cores" vary in time and from person to person, how compelling their voices are, finding patterns in their outputs, etc. Can someone explain what problem metaethics is supposed to solve?