Why do people get so mad when someone professes they are Agnostic?

Why do people get so ticked off about someone saying they are Agnostic? I mean, why is it so absurd to say "I think there COULD be a God but I don't think we will ever know for sure or there may never be a way of knowing if He exists or not."? I mean think about it. Should be so nieve to believe everything other people say or what is written in books, which by the way is written by man, as the authorative truth? Has anyone seen God? Has anyone died and seen the afterlife to tell us about it? Oh wait...I forgot..the Bible is enough proof. Riiiight. Well, I guess that means that the Kuran, the Kabbalah, the Tao Te Ching and everything else ever written is ALSO the truth. This "question" I posted may stir up things and that isn't my intentions. I am simply trying to get different perspectives on Agnosticism in the hopes that maybe I can learn something as well.