This 'criticism' is one that can be made of any analysis of morality.
— Bartricks
How can you be so sure? And if it were so, one would have to question every prescriptive moral theory. One must then not be afraid of doing so. — spirit-salamander
Well, I showed you how it would apply to non-naturalism. Nothing stops 'the Form of the Good' from issuing a prescription to kill others for fun, does it? So, it applies to non-naturalism.
What about naturalism? Well, if natural features can issue prescriptions - and obviously they cannot, but the naturalist thinks otherwise (or else isn't talking about morality at all) - then what stops the natural world or some relevant part of it (the trees, perhaps) from issuing a prescription to kill others for fun? Nothing. Yet were it to do so, then killing others for fun would be right. So it applies to naturalism.
I take it that you now reject those two kinds of view?
Right, moving on....well, it clearly applies to individual and collectivist subjectivist views, for nothing stops me from issuing a command to others to kill others for fun, and nothing stops a collective from doing the same (apart from the incoherence of thinking that collectives are themselves minds capable of issuing imperatives, of course).
So, I take it that you now reject individual subjectivist views - such as your own - and collectivist subjectivist views?
What about nihilism? Well, most nihilists think that morality is at least capable of existing, they just think it does not. So they think that there is a 'possible world' in which some acts are right and some wrong. But if they admit that there is a possible world in which some acts are right and some wrong, then they should accept that there are other possible worlds in which very different acts are right and wrong, such as killing others for fun. For in these possible worlds one of the above theories about morality will be true, and we've just seen that they can't rule out such possibilities.
So, I take it that you now reject this kind of nihilism as well.
The only view to which the criticism could not be made, would be the view that morality is incoherent and thus is incapable of existing. However, a proponent of that view thinks Hitler actually did nothing wrong. And if one is fine with that view, then it would be somewhat ridiculous to reject views that allow that it is metaphysically possible for Hitler's acts not to be wrong, but that they were in fact very wrong indeed, wouldn't it?!? So I take it that you reject that view too.
So, the criticism can be made of all alternatives worth considering. And it is my view and mine alone that can deal with it.
Note, you are now in the incoherent position of having rejected all possible views about the nature of morality. So, if you are logical, you will now realize that something must be wrong with the criticism, for they can't all be false.