Sorry Nevo for the tardy reply.
I don't think you get to keep using D&C 20:5 in the way you are. For clarity's sake, I'll quote that verse here.
5 After it was truly manifested unto this first elder that he had received a remission of his sins, he was entangled again in the vanities of the world;
That doesn't specifically reference the First Vision. How many LDS would believe they had been forgiven of their sins, and only claim a good feeling as confirmation? Why does this manifestation of forgiveness imply a direct visitation by Jesus and God?
Your argument is begging the question. You assume that the First Vision was known prior to D&C 20:5 being written, and references it. But you are using this verse as evidence that the First Vision was known at the time D&C 20:5 was written in the first place.
Let's try an exercise here. Can you think of any possible interpretations of D&C 20:5 that don't include the First Vision?
At any rate, the point has been made, and not refuted, that the First Vision story was not generally known, apparently, either within or without the church. You have tried to offer some excuses as to why this should actually be the case, but it's not convincing. Joseph's own history, as contained in the canonized scriptures today, talk of a general uproar of all of the sects in his area against him because of his claim. And yet nobody has documented such an uproar - even by those people inclined to be against Joseph from these early days, who brought up many things against Joseph Smith, but never that he'd claimed to see God and Jesus.
Mormonism ceased being a compelling topic for me when I finally came to terms with its transformation from a personality cult into a combination of a real estate company, a SuperPac, and Westboro Baptist Church. - Kishkumen