Many American folk singers have tried to leave their world a better place by writing songs of social protest. Musicians like Woody Guthrie, Leadbelly, Pete Seeger, Bob Dylan, and Joan Baez sang with fierce moral voices to transform what they saw as an uncaring society. But the personal tales of these guitar-toting idealists were often more tangled than the comparatively pure vision their art would suggest. Many singers produced work in the midst...