It seems I cannot improve on my original redress of this difficulty.

I may be sticking my neck out by saying this, but it seems that very little work on this subject has been done in philosophy. It is usually simply assumed what ethics is. In the case of an attempt at a Nazi moral theory, for example, one thing to which Hitler appealed was loyalty to one's race--where loyalty is a recognisable moral value. It makes his theory, if not moral, then at least not absurdly otherwise, because this is a reasonable attempt at a commensurability with our own values. Hence, I guess I can still not improve on the original answer I provided in the thesis, although it seems striking to me that one cannot actually specify what a moral theory is without thereby begging the question in favour of a certain amount of moral content.

Of course, this also begs the question of where our moral values originate, and in this regard, I have two preferred avenues to explore:

• timeless moral imperatives in social functioning; and
  
• human nature, as analysed in evolutionary psychology.
  

I choose the latter. I regard it as more foundational, and this will probably help to explain at least partly why the timeless moral imperatives in social functioning are the way they are. It does not seem anymore that morality can be grounded in society without begging the question in favour of certain social norms, because society and its practices constitutively rely on moral terms to one degree or another. Of course, morality can still be identified in society, through empirical investigation of those same cultural norms. But for a proper grounding of morality, we have to look to human nature for that. I feel, if nothing else, like that kind of investigation will give me some kind of intellectual ammunition the next time that any moral value is called into question. I want to be able to defend it with a cogent explanation as to its likely origin and a justification of why it is the way it is.