How much knowledge should one have (if any) about a religion's texts (bible, Qu'ran etc.) before stating opinions about god?

Please allow me to clarify. I’m kicking back, observing people arguing about religion and god on facebook. Something that caught my attention was a person who pretty much said we can’t properly criticize god unless we know all of the important facts and figures of the bible.

Now, I would understand this if one was arguing about the validity of events in the bible, but this person is suggesting, for example, you can’t claim religion is man-made poppycock because one hasn’t fully comprehended the events of the bible (or Qu’ran etc). One cannot posit the notion that god may or may not exist because that person hasn’t fully understood the bibles references to certain events and questions regarding god etc.

Am I making sense? What do you think? Can one develop a solid opinion about god without extensive knowledge of a religion’s sacred texts?