While I am for relativism in the case of dealing aliens I am the very opposite in the case of us. Human rights are universal. When somebody tries to rationalize monarchy or genital mutilation with tradition he is simply wrong.
Of course the problem of such a stance is that it is on a fundamental level totalitarian. But you need this zero-level of dogmatism, you can e.g. not say that democracy is contingent and we can vote on whether we want it or not. In Germany this was possible eighty years ago and it led to fascism.