I am sincerely curious: are you able to provide a criterion or two that would allow me to make objective moral decisions (the possibility of which I think you are postulating)? How do I know slavery is immoral, besides that it is considered immoral in the given cultural context? I am sure an Athenian gentleman 3rd century BC didn't think that way; Aristotle surely didn't - and he spent a lifetime on systematic reasoning, ethics incuded.