[User23]

> all value propositions necessarily either are directly or rest upon subjective preference

You haven't shown this, so you're just sneaking in the premise that ethics has no objective foundation, which is the very question under consideration. I could just as easily baldly assert "all value propositions necessarily either are directly or rest upon objective foundations," but I'm not because it would be philosophically uninteresting.

I accept that there are no valid ethical premises is a valid conclusion from the absence of an objective ethical authority. I can only abductively conclude the existence of such an authority because it appears to me that ethics is not in fact a degenerate science that can produce any result whatsoever.