why might someone choose evil over good?

One of the themes of Golding's book is that people are drawn to the darker side of human nature. Most of the boys find it easier and more "fun" to be destructive and violent than to be constructive and peaceful. It is only Simon that understands the darkness of man's heart.

“However Simon thought of the beast, there rose before his inward sight the picture of a human at once heroic and sick.”