"Why ought people do what morality requires? The honest answer, I think, is that they ought to do it only if they care about the well-being of others; wish to live in harmony with them; want to avoid a life likely to be solitary, nasty, brutish, and short; are moved by examples of good lives; and are repelled by examples of evil ones. Such people are the friends of humanity. Humanity also has its enemies, and that is what evildoers indifferent to the moral "ought" are. It is important to bear in mind that evildoers are not mere backsliders who lie, steal, or cheat, but people whose actions cause monstrous harm. They do not just violate moral limits, but reveal a depraved attitude toward them. They are the sort of people who snatch an old woman from her deathbed in order to burn her alive, like the crusaders; who enjoy a cozy lunch between two bouts of mass murder, like Stangl; and who incite a mob to dismember and cannibalize live victims on mere suspicion of political dissent, like Robespierre. To think of such evildoers as enemies of humanity is not too strong a condemnation and to treat them as such is well deserved. ..."

- from John Kekes' (2005) The Roots of Evil, Cornell University Press, pg. 198. A well-argued book, sobering, clear-sighted and unromantic, although perhaps Kekes pays too little heed to  psychopathy as a disease. Not least among the book's virtues is simply being a university-press book that is actually readable.