It would appear the OP’s questions were meant to elevate Catholicism at the expense of Protestantism by showing Protestantism to be inconsistent at best, and therefore fallible, making it unrepresentative of divine truth. Whereas, by implication, Catholicism is infallible due to 1) its direct link to Christ, who was infallible by definition, and 2) its consistency over the past 2,000 years because the Catholic Church follows Sacred Scripture, Sacred Tradition, and the Sacred Magisterium, whereas Protestantism does not.
In this context, the Sacred Magisterium is the teaching authority of the Church in which the task of interpreting the Word of God is entrusted to the Pope and to the bishops in communion with him. To leave this task to anyone else would lead to immediate fallibility and error. Thus, Catholicism considers the laity, including Protestant ministers, to be incapable of divining the true Word of God—a task best left to the Pope and the Vatican.
From a practical standpoint, infallibility is the immunity from fallacy or liability to error of any kind in expounding upon matters of Christian faith and morals by virtue of the promise made by Christ to Peter and the Church. Because of this divine promise, any Pope is preserved from the possibility of error (papal infallibility) in the exercise of his office as shepherd and teacher of all Christians. Moreover, because of his supreme apostolic authority, any Pope defines all doctrine concerning faith and morals for the entire Church. Of course, the infallible teachings of the Pope must be based on, or at least not contradict, Sacred Tradition or Sacred Scripture.
Please remember that any pope is now carefully chosen by the College of Cardinals whose members go through extensive soul searching, prayer, reading of Sacred Scripture, and divine revelation to arrive at their final decision. One could argue that this process is one of the most deliberative undertakings known to man, and is, in itself, infallible.
Yet, despite all of this infallibility, even the most casual observer would have to admit that the Catholic Church, led by past popes, has made some colossal blunders. Here are a few examples:
Holy Land Crusades
Pope Urban II authorized the First Crusade of 1095. Throughout the Crusades, hundreds of thousands, if not millions, were killed because of Catholic Church involvement and approval.
Other Mass Killings
In 1209, Pope Innocent III preached crusade against French rebels. In 1572, about 20,000 Huguenots in France were killed on command of Pope Pius V.
Inquisition
In 1252, Pope Innocent IV issued a papal bull entitled Ad exstirpanda, which authorized the use of torture by inquisitors during the Inquisition.
Slavery
St. Augustine argued that slavery was not absolutely forbidden by natural law. Thomas Aquinas argued the case for slavery subject to certain restrictions. Pope Paul III sanctioned the enslavement of baptized Christians in Rome. In the early thirteenth century, official support for slavery and the slave trade was incorporated into Canon Law (Corpus Iuris Canonici), by Pope Gregory IX. Pope Martin V authorized a crusade against Africa in 1418 and this was coupled with a later bull (1441) that sanctioned the Portuguese trade in African slaves.
To be fair, no fewer than twelve popes rightly condemned slavery. By doing so, however, these enlightened pontiffs were not in accord with other papal decisions, constituting, at the very least, papal inconsistency over time as the Catholic Church struggled with the issue of slavery.
Can we at least agree that the truth never changes; that is, what was true yesterday is true today and will be true tomorrow? For example, slavery should always be seen as wrong and immoral, and this position should never change if it’s true. If we can’t agree, then we are admitting that truth is mutable and subject to interpretation. In any event, perhaps the Catholic Church doesn’t have a monopoly on the truth after all, and maybe we have to admit that the Church has changed its mind on important matters, such as waging war on Islam, massacre, torture, and slavery, and will continue to do so, making the Church a fallible organization indeed.