You could be wrong about morality itself.
What sort of impact would being right or wrong about morality have that I could notice? For example, let's say someone thinks taxation is inherently morally wrong. What sort of observations are ruled out by this belief, such that making those observations would falsify the belief?
The questions is what you should care about.
Is it rational to care more about being able to predict accurately than care about inadvertantly doing evil?
Derek Parfit has published his second book, "On What Matters". Here are reviews by Tyler Cowen and Peter Singer.