the proverbial jury is metaphorically out!

this is more of a question, probably to Dan NJ more than anyone else... but anyone who is up for answering, should!

just to set the pretext for the question, so that i am not misunderstood:
i do not necessarily disagree (or agree) with DNJ's theology... it is a question about authority...

if one makes a statement like "the language of genesis is not like a scientific book", where does that information come from (for either argument)?
why did we first come up with the idea that genesis (as an example) is a historical account; was it the early church wanting to keep "tabs" on its followers (control...)?
conversely, why do we ("they") think that genesis is not an historical account...?

is it from the original text, and the actual language, prose (and other arty-farty things that i, as a physicist, have no concept of;) ), or is it just something that we are told. this question must be posed to both camps of the argument

then the question is just as easily applied to the NT books that have recently been discussed in Theology 2.0!

dont get me wrong, i dont necessarily disagree with genesis being historical, but i would like to know why there is a consensus either way...

the proverbial jury is metaphorically out!