First, from our cultural distance, it is evident that Kant's arguments against masturbation, for the return of wives to abusive husbands, etc., are gobbledy-gook. This should make us suspicious that there might be other parts of Kant, too, that are gobbledy-gook, for example, the stuff that transparently reads like gobbledy-gook, such as the transcendental deduction, and such as his claims that his various obviously non-equivalent formulations of the fundamental principle of morality are in fact "so many formulations of precisely the same law" (Groundwork, 4:436, Zweig trans.). I read Kant as a master at promising philosophers what they want and then thowing up a haze of words with glimmers enough of hope that readers can convince themselves that there is something profound underneath.Okay, well that's taking him down a notch! But now he draws conclusions about us.
Second, we cannot expect ordinary people to be better philosophical moral reasoners than Kant. Kant's philosophical moral reasoning appears mainly to have confirmed his prejudices and the ideas inherited from his culture. Therefore, we should be nervous about expecting more from the philosophical moral reasoning of people less philosophically capable than Kant.Here's the thing, though. Kant is grandiose. You can practically hear the trumpets blaring in the background. There's a lot of systematizing and beholding the amazingness of mankind, and heavy breathing amid all the brilliance. Perhaps the trumpets etc. got in the way of clear thinking. So--take heart! When we're thinking more plainly about moral matters, it's not impossible that we do better than Kant, despite Kant being ... Kant.