metaethical negativism and ethical exhortation

In this post I want to consider whether something inconsistent is happening when someone simultaneously makes strong substantive ethical assertions – assertions about what they and other people ought to do in a specific scenario, what “the good” might be in general, whatever – and makes strong negative metaethical assertions. By a negative metaethical assertion I mean specifically one of four assertion types: non-cognitivist assertions that moral statements don’t express propositions; error-theoretical assertions that all moral statements are false; anti–realist assertions that there are no moral facts; and moral-skepticist assertions that there is no one knows anything about what’s right and wrong, and therefore that no one can justify any moral statements.