If morality is totally non-predictive then it shouldn't be in our model of the world. It's like the sort of "consciousness" where in the non-conscious zombie universe, philosophers write the exact same papers about consciousness despite not being conscious. If morality is non-predictive, then even if we act morally, it's for reasons totally divorced from morality! If morality is non-predictive, then when we try to act morally we might as well just flip a coin, because no causal process can access "morality"! That's why morality has to predict things, and that's why it has to be inside peoples' heads. Because if it ain't in peoples' heads to start with, there's no magical process that puts it there.
If morality is totally non-predictive then it shouldn't be in our model of the world.
The point of morality is to change the world, not model it.
If morality is non-predictive, then even if we act morally, it's for reasons totally divorced from morality!
If we act morally, the morality we are acting on predicts our actions. Your beef seems to be with the idea that morality is not some universal causal law -- that you have to choose it. There will be a causal explanation of behaviour at the neuronal level, but that doesn't exclude an explanation at the ...
Derek Parfit has published his second book, "On What Matters". Here are reviews by Tyler Cowen and Peter Singer.