Kant's argument [...] cannot and need not rest on the claim that all these alternatives to his interpretation of rational action can be conclusively refuted. It involves only the claim that his interpretation is more natural and reasonable than they are. I also think that so understood, Kant's argument does as much as can possibly be required of any argument purporting to establish a claim about what has ultimate value. In philosophy, as Aristotle wisely tells us, we must not apply the wrong standards to a subject matter (Aristotle 1094b25). This also means we must not expect more of a claim, or an argument for it, than is reasonable.

Kantian Ethics (2008) - Ch. 5. Humanity