Content warning: This book contains multiple accounts of sexual abuse and murder, which are discussed in this section.

Krakauer asserts throughout the book that religious belief is, at its core, irrational and that it lends itself to extremism. Krakauer suggests that Ron and Dan Lafferty are on a long list of religious extremists, including Osama bin Laden, David Koresh, and Jim Jones. Similarly, Krakauer explores the history of Joseph Smith and the Mormon faith and implies that religious extremism was prevalent at the religion’s inception. In the prologue, Krakauer questions how a “sane and avowedly pious man,” such as one of the Lafferty brothers, could commit such a heinous crime. He suggests that the answer is the abandonment of rational thinking. In Chapter 2, Krakauer refers to religion scholar Philip Jenkins who argues that American extremism is such an important part of the country’s history that it can never be described as being fringe.

Krakauer shows that almost as soon as the Mormon Church was born, religious sects began to splinter off, many of which perpetuated extremist views. Krakauer also revealed how Joseph Smith himself held extremist views, including blood atonement and plural marriage, and performed extremist actions, such as when Smith took underage girls as his plural wives.