I see the problem stemming from some other date than that listed in the poll. The beginning and solidification of the Magisterium, and with that the advent of Sacred Tradition, which stood equal to Scriptural Revelation in the eyes of the Church, were the leading edge of "going wrong."
God seems to have wanted a local body of believers who would each be regenerate, and responsive to the leadership of the Holy Spirit in accordance with the Word, but this was supplanted in the hierarchical Magisterium of the RCC, who had a great need to consolidate power with the advent of State approval so as to eliminate rivals and institute what they saw as God's Kingdom on earth.
Interesting is the fact that the term Magisterium derives from the Latin, which was not even a major force in the early church until around circa AD 300. But the early Magisterium was still made up of regional Bishops until another hundred years had passed.
Pope Leo (circa AD 445) made the decision that the Roman bishop (or "papias" = Pope) would be the preeminent figure in the Church. It was Leo I who first pressed forward the concept that Peter was the first Pope (Petrine Supremacy), and the revision of early church history began at that moment. Sacred Tradition, being held in the hands of the Roman Pope, and interpreted almost fully by him, and the suppression of the Word, led to excesses in the church, changes in the baptismal structure, and eventually the payment of penance, indulgences, the sacramental system (as codified), and other non-Scriptural doctrines led the Church into a place where it stood against the very Word that formed it.