The following simple and valid argument came out of discussions with Mark Murphy (who has a forthcoming book that contains related arguments, though perhaps not this one).
According to the identity version of Divine Command Metaethics (IDCM), to be obligated to A is to be commanded to A by God (or to be willed to A by God or to be commanded to A by a loving God--details of this sort won't matter). But:
- If p explains x's being F, and to be F is the same as to be G, then p explains x's being G.
- My being commanded by God to follow Christ explains my being obligated to follow Christ.
- It is not the case that my being commanded by God to follow Christ explains my being commanded by God to follow Christ.
- Therefore, it is false that to be obligated to A is the same as to be commanded by God to A. (By 1-3)
The argument more generally shows that no normative-level answer to a "Why am I obligated to A?" question can provide a property identical with being obligated. Thus, sometimes at least the answer to "Why am I obligated to A?" is that Aing maximizes utility. Hence, by an exactly parallel argument, being obligated to A is not the same as having A as one's utility maximizing option.
The argument is compatible with constitution versions of DCM on which the property of being obligated to A is constituted by the property of being commanded to A. But such theorists then have the added complication of explaining what the constitution relation means here, over and beyond bidirectional entailment (after all, many non-divine-command theorists will agree that necessarily x is obligated to A iff God wills x to A).