This is a truly excellent post, thanks very much. My mind was leaping ahead to the last paragraph but three long before I got there.

You think it could be a cult? Put aside for a moment the question of whether or not their Big Idea is the real thing. Are they acting in a requisitely rational manner? If so, by all means put on a robe. If not, smile and back away.

To that end, does anyone have an example of some followers of an Irrational Big Idea conducting their society/group in a comparatively rational/non-cultish manner (aside from that belief)? If there's no cult-essence that comes with Faith-In-Big-Idea, there must be a couple of notables. (And no, you get no points for any of; Singularity, Transhumanism, Life Extension or Head-Freezing!)