ISIS and Eric Hoffer

Two things Eric Hoffer said struck me as particularly relevant to the ISIS phenomenon.

From Wiki:
Hoffer argued that fanatical and extremist cultural movements, whether religious or political, arose under predictable circumstances: when large numbers of people come to believe that their individual lives are worthless and ruined, that the modern world is irreparably corrupt, and that hope lies only in joining a larger group that demands radical changes.

And something he's quoted as saying-
"You can discover what your enemy fears most by observing the means he uses to frighten you."

So the ISIS tactic of public atrocity and public execution, and their taking and selling their female captives as chattel, is a good indicator that it is precisely such things that they fear most.