Perhaps I’m not fully grasping your angle, but if ethical valuations exist in the same way that gastronomic, sport, partner, pet, and fashion valuations (preferences) exist, then what is the basis for elevating them above the rest? It can’t be the existence of functional explanations as I’m sure there are plenty of functional explanations for most other valuation/preference realms. I’d bet there’s an evolutionary explanation for why most people dislike bitter food (essentially, evolutionary gastronomics).
Since objective (agent-independent) morals/ethics clearly don’t exist, the subjective ones are a mere subset of all possible valuation/preference realms, and I can see how someone would call them “nonsense” in the same way they’d call pizza valuations/preferences nonsense. Obviously, no subjective valuation/preference is “nonsense” to the subject that’s making it.