You seem to think that anyone who thinks carefully enough will agree with you that there is some set of core meta-ethical principles that acts as an attractor in a dynamic process of reflective updating. I disagree with this. There is no core attractor, and the dynamic process is not one of -better and better thinking as time goes on.

How can we know whether that is true or not? If we had access to multiple mature alien races, and could examine their moral systems, that might be a reasonable conclusion - if they were all very different. However, until then, the moral systems we can see are primitive - and any such conclusions would seem to be premature.