One of Kant's most enduring ideas might be his thoughts on evil, specifically, there is no such thing as demonic evil. This to me is confirmed by not only his idealism but later materialist work, be it Freud or Marx or what have you. At worst, human beings do not even entertain themselves with the fantasy that they are trying to do good, they are self-knowingly acting for themselves. That is, they do not even try to tell themselves what is good for me is good for all, they just want to seek their own happiness at the cost of all others, to make them into mere means, etc. This is still evil, to Kant, but not demonic evil. Kant shows would have to be some sort of free and necessary act, which is yet contrary to the moral law. As Hegel puts it, nature is free and contingent, the notion is free and necessary. It is a similar thought as Rodl in "Good, evil, and the necessity of an act". It is also why Kant says that humans have a predisposition to the good, whereas we only have a propensity to evil, a propensity is more thought of something we can at least logically imagine is not necessary for the concept of the human being, for example, Jesus Christ or the moral sage. Freud's work goes even further to dispel this idea of pure or demonic evil. The traumatized person for Freud can work through that event in so many ways. One example might be the child that is abused, verbally or physically at home, and starts acting that event out in some way at school on his peers who they were once friendly to. To their peers, the new behavior seems bizarre, unwarranted, and just evil. Everyone has their own issues, their own fantasy, and things that drive them to do what they do as they strive for pleasure. This may cause them to play that out on people they know and those they do not know, it may even be how people relate to the world at large, and for those who are in positions of power and influence. I do not know what work the idea of demonic or pure evil does for people, you see it in the naive hero vs villain dichotomies over and over. It might be comforting for some to think of demonic evil as necessary and contingent, but for Hegel and for Kant that is just nature, which is not evil. No learned theologian entertains this idea as far as I know because the next step is always the discussion of theodicy it seems, why would evil be allowed, natural or human?