I think of my dad as a very smart man. I thought he could do anything. He read and continued to learn for most of his life. When I was a kid he was the person I went to with almost all of my questions. As a kid I enjoyed reading Dad's Popular Science magazines, all of his magazines, really, and all of his books.
So when I wanted to understand a thing, Dad was my go to guy. He nearly always knew the answers or he knew where to go for answers. And that included questions about God and religion.
Dad was raised a Catholic and considered himself a Catholic all of his life. And I find that curious, you know? When I would ask Dad about religious quandaries he would have answers. From my questions as a small child to my questions as I got older, Dad had answers. ANSWERS to questions like, How could God ask Abraham to kill his beloved son. What about the people who lived before the Savior was born? What is Limbo? What is the difference between a religion and a cult? Why can't women be priests? How does transubstantiation work? Do we have a soul? How does that work? Why don't other religions do communion the way we do? What does it mean to be Jewish? Why should I avoid people who are different from me? Why can't I read that? Why is going to that church wrong?
He fed me the hardline religious answers to all of these questions. When I think of it now, I wonder how someone smart like my dad could believe such nonsense.
As I became an atheist and it seemed so obvious, I felt certain that Dad, too, smart as he was, had figured it out. But he had not. He was very upset with my apostasy, very upset. And now, his death several years ago, I must ask the question How can smart people believe this stuff? How could Dad, with all of his reading and science knowledge hold on to the fairytale stories told in childhood?
I know you are thinking of Michael Shermer's book Why People Believe Weird Things: Pseudoscience, Superstition, and Other Confusions of Our Times, as well as some of his other books on skepticism. I've not read any of Shermer's books, though I've heard a few talks by him. Something I listened to recently on The Thinking Atheist podcast attempted to offer some answers to the question Why? Why would otherwise smart people continue to believe religious dogmas?
One interesting idea is that very smart people tend to fall prey to confirmation bias because they are so smart and are better able to come up with explanations for their weird beliefs. I can see that Dad might fit into that category. Maybe.
You might also enjoy:
The Hideous Dance Between Faith and Critical Thinking
Your Life Has No Meaning
Growing Up Godless