Who here has no false beliefs?
Put your hands down! Everyone has some false beliefs. Now, what got me thinking on this was the fact that I saw a comment on someone's blog outlining (his description, at any rate) paranoid schizophrenia. But, if you eliminate all the "sometimes associated with" items, you are left with the rational response to a (possibly false) belief that a secretive group was trying to eliminate one's self. But, we know secretive groups exist and blend seamlessly in with society. Although unlikely, it is possible to be a target of a secret group. And that could even be the result of some unfortunate chance.
There seems to be a trend to label as "crazy" anyone who holds disapproved beliefs. My own thought is that this is a symptom of people not wanting to hear dissent against their core beliefs. It is a way to discount alternate perspectives. While there really is such a thing as madness, it entails a worldview that is incoherent, not simply incorrect. It would be a set of beliefs that produce inconsistencies on a regular basis, leaving the individual unable to act.