Such factors could at most be relevant in excusing me for the nonperformance of my duty.
On another interpretation, however, Kant may well be mistaken.
Although it makes (in a reasonably clear way) some important distinctions, it also contains much that is obscure and, as an introduction to what is actually to follow, somewhat misleading.
One thing is reasonably clear: Kant is at some level worried about the moral philistine -- the businessman, the politician, the military officer who prides himself on his role as a hard-headed, no-nonsense, realistic and who, in pursuing his objective of greed or power or victory, either ridicules morality and moral theory as irrelevant to his practice or who conveniently adopts an account of morality exactly tailored to allow him to do whatever he pleases.
It is not unreasonable to suggest, for example, that the proper specification of the moral duty itself may sometimes quite properly take account of empirical variations in circumstances.
Consider, for example, the duties that we have -- in both morality and law -- to do what is Etiquette, unlike morality, is taught as a rigid set of rules that are on occasion to be broken. Moral rules are not taught as rigid rules that it is sometimes right to ignore; rather we teach that it is sometimes morally permissible to tell lies (social lies), break promises (as e.g.
(Such notions as "it's just business" or "it's just politics" or "military necessity" might function in this way.) This is the person who, when met with a challenge from the realm of moral principle, tends to respond dismissively with the smug clich "yes, what you say may be true enough in theory, but it doesn't apply in practice." What worries Kant the philosopher even more than these moral philistines, however, is the existence of philosophical doctrines that can be used to give a cover of intellectual respectability to the iniquities and deceptions practiced by such persons.
There is very little that a philosopher can do directly to combat ordinary human venality and self-deception, but the philosopher can properly assume the task of unmasking the intellectual pretensions of those who would use or misuse philosophical doctrines in support of venality and self-deception.
(This gap is one that, I would argue, faces the utilitarian much more dramatically than it does the Kantian; and demonstrating the gap is surely the main point of all the well-known scapegoat and other counterexamples to utilitarianism.
As clever as Kant's suggestion is, however, it surely does not address all aspects of the theory/practice challenge to morality.