Good and evil are a potential that lie within the heart of each individual; but a believer in an ideology can feel morally justified in perpetrating cruelty towards others, because he sees himself as defending a higher value against an infidel.
Notes
Note: contact me if you know what this article is from. As it opens with "In the last chapter, we have seen..." it must be from a longer work, but I don't know what. [-J.W., 2011]