Moral
principles can never have the same foundations as
natural science.
But I am not entirely convinced that moral principles cannot be
derived from a combination of conceptual analysis and various premises
that are not themselves controversial.
There are philosophers like Alan Gewirth who have argued
for human rights in a way that is independent of our attitudes and
choices.
Right now this isn't important because we are assuming that some
form of ethical relativism is a correct meta-ethical theory. But in
the larger picture, I think this is an important issue.