Why do people think putting "It was written" before a statement gives it instant credibility?

Seriously... why do some people behave as if adding "it was written" to any ignorant, incendiary statement lends it credibility? By that logic the claim, "It was written that you must nibble the root and fannangle the wangle" is gospel. It doesn't matter that it was written in a graphic novel entitled 'Johnny the Homicidal Maniac' or that I ingested psychedelic mushrooms prior to reading it. (this question was prompted by an answer to another or my, seemingly innocent questions, someone wrote 'it was written that all nations will turn against Israel' and, well, it just kinda bothered me)