Great thoughts, and I think the Charles Manson comparison is legit enough.
I guess the difference would be that, Manson's methods of overwhelming and taking hold of a person's entire psychic existence were deeply personal (and with the women, sexual), and therefore a small following was the best he could ever hope for. Those infamous crazy-piercing brown/black eyes and all. FF's charisma came not from having a piercing, I-OWN-you stare nor an ability to gain complete psychological control of a small group of people, but rather a unique and bizarre set of circumstances that combined to put an intelligent and studious yet extremely kooky man from Kentucky at the head of an international, boisterous, and apocalyptic religious sect whose very existence RELIED upon an always immenent doomsday in the minds of the flock, and Fred's hypnotic (to the impressionable) writing style was just the trick.
Two men with different styles and different circumstances, but with the same bent towards believing themselves to be at the very heart of a grand cosmic drama that was being played out. You can throw Hitler and David Koresh and countless other into that category.