Some essential ideas about the nature of morality are survivals of Judaic-Christian ideas, and function now outside the framework of thought that made them intelligible. Our ideas of the moral self, human dignity, and the Kantian summum bonum also survive from an earlier conception of theistic ethics. All these ideas became “self-evident” and essential elements of our secular moral discourse, but they belong to theistic metaphysics and do not easily fit into secular metaphysical naturalism.
Secular moral philosophers are confronted with the following dilemma: since the moral discourse is useful and confirms our deepest moral intuitions, doing away with it incurs a cost; a price is also paid for keeping a flawed discourse, for “truth” is a very valuable commodity. It is not always the most reasonable thing to drop the theistic elements of moral discourse; instead the stance of moral fictionalism makes it possible to keep a discourse while knowing that it is inherently flawed.