h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I must say that I lean toward Relativity. For in a dark world, a pen-light may seem as bright as the sun does in our world. Either that or as an advantage system, or as J.K.Rowling put it, 'There is no good or evil. Only power and those too weak to get it.' (Quote may not be completely accurate.) The ideas of Good and Evil just seem too 'black and white', 'comic-book' to me.

So much of what has been said about evil, good or relativity seems to be wandering from the basic point that these are concepts, not actualities. The previous entry refered to power, in a general sense without defining it, again only a concept not actuality. Power when defined say by an engineer or scientist as the rate of doing work say in horse power or some more modern units has a meaning which can be discussed or understood. Unless secifically defined, the concept has no specific identity or meaning.
In practice these concepts need to be seen in a cultural setting that defines their limitations and asumes a good or adequate understanging of the associated mechanisms. Thus we may consider it "good" to say, heat some food to kill some bacteria and not give ourselves or others food poisoning, but recognise that it is only by eating some bacteria (but maybe not too much), that we develop tolerance to that bacteria. In some other context it would normally be considered "wrong" to kill. But to apply this , we need this "relatively" sophisticated understanding and the "power" or better expressed ability to produce controlled heat. Easy you may say in a modern kitchen with a refridgerator and cooker, but put your average 21st. centry person lost in a forest with a smelly animal carcase and no knife and they may well die for lack of the required abilities. We need to remember that good and bad, or evil are moral constructs; and that the true definition of moral is that which is customary, not that which is "right".

JK Rowling was not herself defining what she believes evil is. She was defining one of the characters in her book as evil, by having him say that.