Ayn Rand is often villified for her belief that Kant was "the most evil man in history." Interestingly, Ludwig von Mises (a Kantian of sorts) said the following about Kant's ethics --
"Engels called the German Labour Movement the heir to the German classical philosophy. It would be more correct to say that German (not only Marxian) Socialism represents the decadence of the school of idealist philosophy. Socialism owes the dominion it won over the German mind to the idea of society as conceived by the great German thinkers. Out of Kant's mysticism of duty and Hegel's deification of the State it is easy to trace the development of socialist thought; Fichte is already a socialist."
"In recent decades the revival of Kantian criticism, that much praised achievement of German philosophy, has benefited Socialism also. The Neo-Kantians, especially Friedrich Albert Lange and Hermann Cohen, have declared themselves socialists. Simultaneously Marxians have tried to reconcile Marxism with the New Criticism. Ever since the philosophical foundations of Marxism have shown signs of cracking, attempts to find in critical philosophy support for socialist ideas have multiplied."
"The weakest part of Kant's system is his ethics. Although they are vitalized by his mighty intellect, the grandeur of individual concepts does not blind us to the fact that his starting-point is unfortunately chosen and his fundamental conception a mistaken one. His desperate attempt to uproot Eudaemonism has failed. In ethics, Bentham, Mill, and Feuerbach triumph over Kant. The social philosophy of his contemporaries, Ferguson and Adam Smith, left him untouched. Economics remained foreign to him. All his perception of social problems suffers from these deficiencies."