From this clip:
[Bob Marley] had this idea. Kind of a virologist idea. He believed that you can cure racism and hate; litterally cure it, by injecting music and love into people's lives. When he was scheduled to preform at a peace rally, a gun man came to his house and shot him down. Two days later he walked on stage and sang. Somebody asked him, "Why?" He said, "The people who are trying to make the world worse are not taking a day off. How can I? Light up the darkness."