I think if you read post 53 it might make more sense?
Post # 53 makes no sense whatsoever. Go read it again yourself and you will see the statement "but infallibility merely implies exemption from liability to error. God is not the author of a merely infallible, as He is of an inspired, utterance; the former remains a merely human document." Think about it. An infallible document is "merely a human document"?
The Catholic Church proclaims that "ex Cathedra" means that it is "infallible". There is only one who is "infallible" and that is God.
That causes all kinds of problems for Catholics as the original "ex Cathedra" statements have been pretty much nullified by later statements from the Church. How can the "Church" change "infallible" statements without issuing and "ex Cathedra" statement changing the earlier pronouncement? That leaves Catholics with the obligation to believe that only those "in subjection to the pope" as saved.