Hi Terence

I’m not sure I follow your argument completely, so correct me if I seem to be missing the point.

I take the core of your argument to be the statement  “…If there is no moral system that an amoralist can be argued into - such that for them to reject the argument would be irrational - it may well be concluded that all moral systems are unjustified…”

I suppose there might be two objections to this.

(1)   (A rather frivolous point probably): One might imagine that there could be a moral system which has not yet occurred to the amoralist or his interlocutor – which the former might accept if he knew about it.

(2)   (A more substantial point but one that, I suspect, might not appeal to you): Is it really the case that a moral system is justified just because it is rational?  Because, in fact, when we look back at human history, the most powerful and widely accepted moral systems – including the Christian one on whose remnants we still largely rely – are not notably rational at all. Perhaps morals are, in the end, driven by something deeper than reason?

DA