• Is extremism concerned with the supremacy of one’s own group, or is it defined by hatred of the “other”?
• Do extremists emerge on the scene suddenly, or do they evolve from mainstream movements?
• Are they found only on the margins of society?
• Is violence a necessary component of extremism?
• How do extremists decide on their beliefs?
• Are they rational?
• How can we define extremism objectively when so many possible variations exist?

Berger, J. M. Extremism (MIT Press Essential Knowledge series). The MIT Press. Kindle Edition.