In this relation the human individual makes himself into a thing, which is contrary to the right of humanity in his own person. This, however, is only possible under the one condition, that as the one person is acquired by the other as a thing, that same person also equally acquires the other reciprocally, and thus regains and reestablishes the rational personality.is what he actually thought, then perhaps it is good that he never married. Wikipedia says he did have friends, though. Schiller wrote "Problem: Gladly I serve my friends, but alas I do it with pleasure. Hence I am plagued with doubts that I am not a virtuous person. Reply: Sure, your only resource is to try to despise them entirely. And then with aversion to do what your duty enjoins you."
From what I read his "Pure Reason" seems to treat man as a kind of abstract geometry; a formless point with no shape.
Using that kind of model of people as the foundation for morality and duty is an absolute minimum. A morality that deals with real people cannot help but include other rules suitable to the details of the nature of real people.
For starters: "It is not good for man to be alone." Experience with solitary confinement in prison shows that being alone can have horrible effects on people. You can think of others.
Even for the point-like rational beings, when he wrote that one should act according to rules that one would be willing to see as universal rules, he required what is not completely possible. Said "point-like rational beings" have finite intelligence. By Godel, when they devise a set of guidelines for determining the value of rules they cannot prove the correctness of every possible rule governing all the permutations of PLRB interactions. There will always be some interaction that the PLRB's rules won't cover. His prescription is incomplete: both on the face of it and because it doesn't address details of the nature of humans.