What kind of idiot falls for a conspiracy theory? Somebody gullible, you might imagine: at best someone vulnerable or mentally unwell, and at worst someone actively malicious. But mostly, to be blunt, not perfectly normal people like you and me. We are too rational, we tell ourselves smugly, to fall for some old guff about lizard people running the world, or Bill Gates wanting to microchip everyone, or the royal family secretly bumping off Diana, Princess of Wales. We go where the evidence takes us, follow the news closely, exercise our own judgment. The bad news for those of us...