why is "truth"--or the lack thereof--so scary?

"Brian McLaren scares me. It isn't his ambiguity on the question of [you name it] that worries me so much as it is his reckless passion for ambiguity in the first place, and his utter fear that someone, anyone, will take offense for any reason; the larger disease of which the first is a symptom."

i hereby post this comment from a blog...and i post it out of context. but it seems to speak to one of the things about "truth" that i find interesting. why is it that "truth," or perhaps "uncertainty about truth" (maybe those are two completely different things), is such a scary thing. why are we so afraid of those who claim to know it? and why are we so afraid of those who claim not to know it?