First, Augustine, although a saint and doctor of the Church was never acknowledged to be infallible. If you pick through enough of his works you will fine numerous errors and positions that shifted and evolved over time. (side question, why do you only cite him when he appears to agree with you and argue loudly against him when he agrees with the Magisterium of the Church?)
The Church did not wait to decide, it proclaimed, ex cathedra, what was a truth that had existed since the beginning of time.
I do not claim "infallibility" for Augustine nor to the magesterium or Pope of the Roman Catholic Church. My use of him, in this matter, was to simply demonstrate that the "dogma" of the sinlessness of Mary was NOT universally held "from the beginning of time". Catholic Theologian Ludwig Ott wrote, “Neither the Greek nor the Latin Fathers explicitly teach the Immaculate Conception of Mary….individual Greek Fathers (e.g., Origen, Basil, John Chrysostom, Cyril of Alexandria) taught that Mary suffered from venial personal faults, such as ambition and vanity." (Ludwig Ott, pp. 201, 203)
BUT...
The Council of Trent declared that Mary was sinless throughout her whole life in 1547.
Pope Pius IX declared the Immaculate Conception on 12-8-1854.
Quite a time gap for insisting something - especially something as important as a specific human other than Jesus having sinless perfection - that contradicts Holy Scripture. If I had to choose between the Bible or a human institution to be my "authority", it would be the Bible because humans are NOT infallible no matter what Bible verses they twist to make it seem they are.
Since you have ventured into this thread once again, will you at least give your opinion of the original article? Do you stand by this Prophetess and her prophecies concerning what "Mary" is telling her will come to pass? I know we get sidetracked in these conversations, but do you have any thoughts about what this poster is trying to warn everyone about?