Although we all know evil when we see it, we are constantly tempted to explain it away or deny its existence, a leading philosopher will argue in a lecture this week.
Lars Svendsen, professor of philosophy at the University of Bergen in Norway, is due to explore the themes of his new book on the "philosophy of evil" at London's Institute of Contemporary Arts on 10 June.
In his earlier published work, he said, he tended to see evil as exciting, "something that transcends the banality of everyday life".
But then history caught up with him and made him view the whole topic as "much more oppressive and sad".
Instead of being fascinated by the "demonic evil" of a few "monsters" such as the Nazis and the serial killers portrayed in many books and films, society needs to recognise that most evil is caused by "people convinced they are doing good" and by "normal, more or less decent, respectable people" - just like us, he added.
Professor Svendsen said he now applauds the views of the French thinker Simone Weil, who wrote that "imaginary evil is romantic and varied; real evil is gloomy, monotonous, barren, boring. Imaginary good is boring; real good is always new, marvellous, intoxicating."
Although we cannot do without the word "evil" - it is much too weak to call events such as the Srebrenica massacre in 1995 "immoral" - he argued that it was also a very dangerous term.
Since the terrorist attacks on the US on 11 September 2001, he suggested, "we have used the evil of others as a justification for our own evil. The genuine evil of terrorism has been used to justify pretty much anything."
Today, argued Professor Svendsen, "there are many attempts to justify evil, which end up denying the reality of evil, although it's something we experience in concrete terms, as when a bomb goes off in the street and kills children."
Theologians who believe in a just God come up with arguments for "seeing evil as part of a greater good and so not really evil", he suggested. And "many political ideologies justify evil as part of historical progress", he added.
Nor does Professor Svendsen plan to let his fellow philosophers off the hook.
"Many philosophical approaches seem to want to get to the root of evil, which means you get lost in abstractions that take on a life of their own," he said.
"Speculation needs to start from and remain in contact with our real experience. Evil is, above all, a concrete, practical problem."
He added: "In absolute terms, there are more slaves in the world today than ever before: million at a conservative estimate. They don't need us to ponder the deeper aspects of divine justice, but to look at how their conditions can be improved."