"The Characteristic Of Gullibility"
Moshe David Tokayer commenting on "Pure And Simple Emunah Is Not A Jewish Concept" :
Reb Tzadok explains that a pesi is someone who believes everything. This is why idol worship is called the height of gullibility (i.e. pesius); for idol worshippers it does not have to make any sense. Our holy Torah, on the other hand, has meaning and makes sense to those who understand.
In other words, emunah peshutah, according to Reb Tzadok, does *not* mean that we must suspend our intellectual faculties to believe things that are absurd.
So how does Reb Tzadok apply emunah peshutah? He brings the Midrash which says that Moshe Rabeinu at the sneh was a pesi. Reb Tzadok explains that if Aristotle had seen the burning bush experience, he would have brought 1,000 reasons to prove that it wasn't God. Moshe Rabeinu, on the other hand, used the characteristic of gullibility to accept that he was witnessing a revelation and having a prophesy.
The point is that even Reb Tzadok who is pro emunah peshutah explains that it is used to bring one closer to God, not to believe the absurd which is a quality of idol worshippers. It is used as an argument to the idol worshippers, "If you believe anything, why not believe the Torah!"