In The True Believer, Eric Hoffer, the longshoreman philosopher, points out that the person who most passionately adopts a cause does so to fill an emptiness within their own life. Any criticism, questioning, or reluctance to join in their particular passionate cause, they take as a personal affront.

Hoffer also points out that The True Believer, the Fanatic, is actually easily converted from one cause to another. Given the right circumstances or motivation, the fanatical Fascist will become a fanatical Communist. Then a fanatical Christian. But—no matter what cause or belief system they embrace and proselytize loudly to others, they will always be a Fanatic.

It is this emptiness within their own psyche, demanding to be filled, that makes them a fanatical adherent to a Cause.

Any Cause.

Don Firth