My first impression upon finishing this book is that the title is wrong. Though Dr. Shermer addresses some issues about why people believe weird things, for the most part this book is more about the weird things people believe, and not so much about the reasons they believe them. For a better discussion about why people believe weird things, I suggest Thomas Gilovich's book "How we know what isn't so."
Shermer devotes all of chapter one to expanding on the definition and characteristics of a skeptic, and all of chapter two to describing science. This lays the bedrock for his future discussions about pseudosciences such as creationism, and helps to make clear the reasons these pseudosciences and superstitions fail to meet the demanding requirements of science. He explains that a skeptic is not synonymous with a cynic. Instead, a skeptic is someone who questions the validity of a particular claim by calling for evidence to prove or disprove it. As such, skepticism is an essential part of the scientific method.
Chapter 3 is a jewel. It describes 25 ways in which thinking goes wrong. Reading this chapter left me wondering if these rules for fallacious reasoning are not encoded somewhere as the rules for participation in some of the more notorious Internet newsgroups devoted to various mythologies.
The second part of the book examines claims of the paranormal, near-death experiences, alien abductions, witch crazes, and cults. Although these stories make interesting reading, they are same examples of debunking we have seen for years. I, for one, would appreciate a fresher skeptical approach that is not so (apparently) reluctant to challenge the claims of institutionalized religions. Is transubstantiation any more credible than claims of the paranormal? Are alien abduction stories any less credible than the Book of Mormon's claims about a large, literate Hebrew society in America 2,000 years ago, that used horse-drawn chariots and steel swords? Are witch crazes any more significant than some Christians who let their children die rather than bringing them proper medical treatment? I think not, and I believe it is time for skeptics to broaden their portfolio beyond the usual array of paranormal activities and alien abductions.
Shermer devotes chapters 9 through 11 to the conflict between creationism and evolution. This section of the book has a wonderful summary of the legal battles fought to keep the religion of creationism out of public schools. Chapter 10 has an excellent description of what is evolution, and a very brief summary of 25 arguments used by creationists against evolution, along with counter arguments used by scientists. Interestingly enough, Shermer offers very little in the way of direct evidence against creationism - of which there is a tremendous amount - and focuses mostly on how to defend evolution. Unfortunately, he has truncated his 25 arguments so much that they are of little practical use - especially against more polished debaters. Shermer admits this at the beginning of the chapter, and does offer an excellent bibliography of more detailed references for the reader.
Shermer's defense of evolution bogs down when he encroaches on the idea that evolution is not a threat to religion. [This is how I interpreted Shermer, though he is not entirely clear about his personal feelings regarding this matter.] Science most certainly is a threat to some religions - creationism, for example (and Shermer argues throughout his book that creationism is a religion - which is why it should not be taught in public schools). It seems obvious to me that sometimes science does threaten religion (more some than others) - but that is religion's problem, not science'. Scientists should stop apologizing for that fact.
In trying to sooth the potential conflict between science and religion, Shermer quotes Stephen J. Gould (one of my favorite authors). Interestingly, Gould (uncharacteristically) offers a spectacular example of some of the bogus reasoning Shermer discredits in chapter 3. Gould says (page 132):
"Unless at least half my colleagues are dunces, there can be - on the most raw and empirical grounds - no conflict between science and religion."
Here, Gould violates Shermer's rule 19 (overreliance on authorities - Gould's colleagues in this case). Then, Gould leaves us wondering if, instead, we are to consider the other half of Gould's colleagues (the half that apparently do not agree with him) as dunces.
To his credit, Shermer provides a definition of religion on page 145 (though he offers no definition of God). I am not sure he makes the matter any clearer by doing so, however, since his definition of religion (as a method) places it as the antithesis of science (also defined as a method). Yet, I got the impression from his book that Shermer agrees (on a fundamental level) that there need not be any disagreement between science and religion.
Part 4 discusses racism and pseudohistory in the case of holocaust deniers. This part seemed out of place in the book primarily because Shermer spends comparatively little time discussing the weirdness of the opposing camp, instead focusing mostly on his perceptions. Though I agree with him on most points, I could no shake the feeling the chapters belong in a different book with a different title.
In the last section (section 5) Shermer gets back on track and finishes with an interesting view of the societal role science plays, and the roll it will play in the future. Shermer holds hope for the human race, in spite of its sometimes-overbearing tendency toward mysticism. He also gives a wonderful summary of why people believe weird things: because it feels good. Though I would like to know more about why it feels good, I cannot argue with his conclusion.
Overall, this was an excellent book. Dr. Shermer is a clear thinker. His ability to focus on the central issues and facts makes this book refreshingly illuminating. His personal touch, brought through stories of actual life experiences, adds to the pleasure of reading his book.