I think a more charitable (and interesting, sociologically) interpretation is that certain Protestant groups want the authority of God to not be vested in a tem

I think a more charitable (and interesting, sociologically) interpretation is that certain Protestant groups want the authority of God to not be vested in a temporal organization like the Catholic Church, and so the book itself serves as a replacement for this. The problem of determining what that means arises then, and not initially from a desire to only follow the book directly.