The moral law is universal.

Many people seem to think that as all do not adopt the moral law then
philosophers like Plato, or his epigone, Kant err on this hallmark of ethics
that moral rules are universal. Many feel that cross cultural studies suggests
to them that moral rules can vary from society to society. They also feel that the
breaking of the moral law by theft or murder by some people in all societies also
shows us that the philosophers badly err.

But neither supposed counter example is really germane, for the flouting
of the moral law does not mean it is not universal, as universal here does not
mean we have all adopted it, but rather that it applies to one and all by the
moraliser. Ethics is about rules, not facts. A flouting of the formal or
categorical moral rule is no more a refutation of it than is any schoolboy
getting his sums wrong in boring mathematical lessons is a refutation of
arithmetic.