You can look at it in one of two ways.

A: A person becomes a paranoid survivalist because he is clinically...well, paranoid. He is mentally ill, a psycho, a whack-job, a nut-case, and if self-medicating his broken psyche by purchasing MREs by the pallet gets him through the day, then good for him.

B: He becomes a paranoid survivalist because it is FUN! We're talking fun toys, here; the weapons, the radios, GPS, camping and hiking gear, and all the other shit associated with survivalism, is fun to play with. It is an expensive hobby, sure, but not as expensive as some. Also, if the zombies ever DO beat down your door, then your $100K collection of Renaissance paintings isn't going to be nearly as useful as my old AK47.