 The first phase of the argument, to  sub-conclusion (3),  is defended by philosophers such as Frank Jackson (1998: ch. 5) and, in more general form, in a non-metaethical context, Jaegwon Kim (1993).  (1)  is presented largely as an intuitive criterion of property identity. Given certain assumptions,  (2)  can be proven just from the claim that the normative supervenes on the natural. This is the claim that there can be no normative difference in how things are without a natural difference in them (see entry on  supervenience).  We won’t walk through the proof here – though see Bader (2017) for a very succinct summary – but consider the following simplified version. Assume – the simplifying step – that the normative property wrongness supervenes on only one natural property: failure to maximize utility. Then, whenever an action instantiates wrongness, it instantiates that natural property, and vice versa – given that the relevant assumptions obtain. And, assuming that supervenience holds with metaphysical necessity, so will this covariation. Wrongness will be necessarily coextensive with the property of being a failure to maximize utility, so (given  premise 1)  it will be identical to that property.