Americans have a complicated relationship with fear. On the one hand, we enjoy fear enough to dedicate a holiday to it. This year, we will spend an estimated $9.1 billion celebrating Halloween. Horror films gross nearly half a billion dollars per year, and are known in Hollywood to have the best return on investment in the movie business. Quasi-dangerous activities like roller coasters are a big industry as well, following Hunter S. Thompson’s famous exhortation, “Faster, faster, until the thrill of speed overcomes the fear of death.” These pursuits are occasions of “fake” fear. They simulate frightening circumstances that lie outside the realm of ordinary life, providing a fun shot of adrenaline without putting anyone in actual danger. Real threats, however, are far less enjoyable. Not even roller-coaster fans look forward to losing their car’s brakes on a steep hill. To enjoy genuine mortal danger is considered abnormal: Indeed, in psychology, the “fear-enjoyment hypothesis” hol...