Most people would agree that it is wise to consider the relevant facts before making important decisions. However, most busy people can't spare the time to analyse every activity or argument in great detail in order to decide if it is rational. Many of us believe, or at least take seriously, various questionable theories or practices, such as astrology, ghosts and hauntings, lake monsters, or abductions by space aliens.
Harrison quotes some surveys which purport to show what percentages of people believe in such things, but is it really that simple? While some people firmly believe, others are merely mildly interested. Also, to test whether or not folk really believe in what Harrison obviously considers false or just ridiculous, is to consider what they actually do. For instance, persons who claim to believe in ghosts, but never read any of the literature on the subject and never visit any allegedly haunted houses could hardly be likely to have any significant belief in them.
Other reviewers have been struck by the tone of Harrison's writing--the impression that he gives of one generously offering the benefits of his superior knowledge and understanding to the benighted lower orders. Some of these folk are actually extremely intelligent and highly educated, but they have one great flaw in that they apparently have various irrational beliefs. In particular, Harrison is horrified by the astronaut Edgar Mitchell who actually walked on the Moon, but gets involved in studying such things as mediumship, hauntings, remote healings, and UFOs, which are deplored by the supremely rational author. Mitchell is a man who examplifies "the inherent gullible nature of humanity".
As I read this book I was irresistibly reminded of some of the science fiction treatments of such characters as Harrison seems to resemble in some ways, such as Star Trek's Spock who often warns Captain Kirk that what he says or proposes to do is "not logical", and Isaac Asimov's robots who, when they are not serving their human masters, are engaged in earnest and totally rational dicussions with one another.
Perhaps if you are prone to engage in irrational thoughts and actions you are eating the wrong kinds of food. Harrison will put you right on this in the section titled "Brain Food". One example is: "half a cup of spinach or kale, quarter cup of blueberries, one strawberry, half a banana, half a carrot, a few nuts, about a teaspoon of flax-seed, three or four ice cubes, and half a cup of water". These are tossed into a blender. Consuming it is a treat, not a duty. (I am not making this up.)
The main flaws of this book are: the confusing coverage of many separate issues, and the strangely frantic and repetitive style of writing. Like many writings by keen sceptics it is often unintentionally funny, so you might get an occasional laugh out of it even if you find it generally a bit tedious to read. -- John Harney.