Very interesting question, @ETpro. I’m sorry it seems so difficult to answer. If I had to hazard a guess (and that’s all I can really do), I’d say it’s a combination of several factors. I think people are born with NPD (they can learn how to overcome it – with a lot of hard work – but most probably don’t. Personality disorders are some of the hardest things to treat successfully). So, they may be hard-wired to think there is a grandiose plan for their lives. If they are also charming and have a flair for sales, they convince several other people of the same. These people become informal ‘followers’, and their adoration feeds the narcissism. Eventually, a doctrine of sorts develops… a natural outcome of the way the ‘leader’ lives his life, and more people are attracted to the group. Adoration feeds narcissism, and both grow exponentially. Now you’ve got yourself a cult.
Up to that point, I think this is all sort of likely, given the right set of people and circumstances. What is really fascinating to me, is how they make the leap from here to mass murder/suicide. Perhaps it’s further grandiosity, “I/we are too good for this world.” Or, could it be that a glimpse of reality has shone through the insanity? If one were to – even briefly – realize that one was wrong, that there was nothing special about themselves, might one reject that reality as strongly as possible? To the point of “death before dishonor”?
Anyway, great question to ponder.