In "In Europe's Shadow," Robert D. Kaplan discusses the dangers of ideological rigidity and intolerance, emphasizing how these attitudes reveal a troubling intensity within human nature. This "beastly core" suggests that extreme enthusiasm can lead people to aggressive or dogmatic behavior, especially when driven by a specific belief system. Kaplan warns of the risks that come with fervent ideologies that promote exclusivity or proselytism.

Moreover, Kaplan conveys the importance of maintaining distance from charismatic leaders or 'prophets' who often attract unwavering devotion. Such figures can manipulate followers, leading to divisiveness and conflict. The book serves as a cautionary tale about the potential for ideological zeal to overshadow reason, highlighting the need for a balanced approach to beliefs in order to foster understanding and coexistence.