moral

Hello Rabbi, since I saw that the Rabbi often mentions Kant’s method of morality, I thought I would ask something about it:
There is an important and very interesting article by Dr. Israel Eldad from the time of the Eichmann trial, which draws a direct line between the Kantian concept of morality (and the “pure understanding”) and the result of Nazism. Can the rabbi explain Kant’s categorical imperative a little more and why such a concept might legitimize such phenomena?
 
Thanks in advance.