The True Believer by Eric Hoffer. I first read this when I was in HS. It wasn't an assignment. I found a copy on my father's desk. He never got it back.
Tim Reynolds
The book evaluates and sometimes disparages communists, fascists, nationalists, and early Christians. Part of Hoffer's thesis is that movements are interchangeable and that fanatics will often flip from one movement to another. Furthermore, Hoffer argues the motivations for mass movements are interchangeable: religious, nationalist and class-based movements tend to behave in the same way and use the same tactics, even when their stated goals or values are diametrically opposed.
http://en.wikipedia.org/wiki/The_True_Believer