It comes down to this:
Once a person has chosen to believe that a certain person is a Tzadik who has no Yetzer HaRah and any of his statements are a direct expression of Divine Will no further discussion (on any matter pertaining to the Tzadik or his teachings) is possible. The strength of such a belief is precisely in the fact that no positive evidence is presented for it and therefore there is nothing to refute. Instead the focus is on wonderous and miraculous stories about the Tzadik. Combine with a personal investment of time and resources and strong social proof and you have the makings of very strong faith which becomes self reinforcing. Make no mistake about it, this formula works.