I think one of the problems of believing the "the end of the world" secarios is that it becomes a vicious circle. The "what if's" are always at the back of your mind, and no matter how much time, money and effort you put into protecting yourself, its never quite enough. As a result of thinking through all the worst senarios, you end up trying to put yourself in a position of total safety - away from everyday life and people, who might if the worst came to the worst, turn against you. In a way its a manifestation of our fear of death.
I can relate to most of the above, however I'm also a realist. We all prepare the best we can, but life is about living, not preparing for some unimaginable catastrophe and a horrific death.
I try and strike a happy balance.
I'm not really sure if that answered your question, but that is my little theory on the mindset of "survivalists". I use that word with caution, and only in relation to my concept of the word - no offence mean't to anyone.