It seems easier to pick on the metaphysics of Christianity, since a belief in God often implies a deity, a person or a conceptualized version of the ultimate. (That is a paradox- how can the infinite be expressed and believed in finitely?) This metaphysical being is not provable either way, and so the cyclical arguments go on.
Yet I can't help but question if they apply to some claims Buddhism makes:
-That there is a cosmic consciousness, super-mind, void, true Self, etc.
-These claims are based on the teacher's experience.
-These claims can be repeated and verified.
-Test these claims empirically, through meditation.
Mystical Christians make similar claims, and from a philosophical or rational standpoint, these would not fall into the same category as blind faith, mythic beliefs or superstitions, nor a general fear of the unknown.
We may strive for security in a universe we do not totally understand, but it is not so much that we have "failed" to know things "out there," as much as we do not see our own identity clearly. Our fear is not of the unknown, it is our own shadows. We project fear into the unknown, and not necessarily the other way. Self preservation, psychological and physical security- these drive us to form ideologies and revert to seeing the world through them. It is only through self understanding, recognizing our unconscious fears, that we can transform our understanding and our action. We must be authentic in order to authentically see the world in a new light. Yet, self-reflection (not intellectual but directly observing ourselves) proves to be the hardest of trials.