surely there's a causal relation between humans' instantiating the computation and Eliezer's referring to it.

Of course there's a causal relation which explains the causal fact of this reference, but this causal explanation is not the same as the moral justification, and it's not appealed to as the moral justification. We shouldn't save babies because-morally it's the human thing to do but because-morally it's the right thing to do. What physically causes us to save the babies is a combination of the logical fact that saving babies is the right thing to do, and the physical fact that we are compelled by those sorts of logical facts. What makes saving the baby the right thing to do is a logical fact about the subject matter of rightness - in this case, a pretty fast and primitive implication from the premises that are baked into that subject matter and which distinguish it from the subject matter of wrongness. The physical fact that humans are compelled by these sorts of logical facts is not one of the facts which makes saving the baby the right thing to do. If I did assert that this physical fact was involved, I would be a moral relativist and I would say the sorts of other things that moral relativists say, like "If we wanted to eat babies, then that would be the right thing to do."