First of all, I'm very happy to have two Catholics onboard to correct me if I'm wrong about anything. The conversation has been less than polite in this thread and it has wandered off the original topic.
Ceeboo, implying that Joseph Smith was an adulter and that he should have been excommunicated, and not explaining yourself better -- That strikes me as picking a fight. You already knew full well that LDS doctrine does not view anything that Joseph Smith ever did as adulterous. If you want to go through that discussion, Private Message me and I'll do my best to establish the LDS point of view on the matter.
As for LDS posts, there have been too many to count that have been very disrespectful. The original post sounded like a question and not a call for trading insults between LDS and non-LDS forum members. Learn some tact or learn to be silent.
So to the point of the original question:
There are two things that are easily misunderstood by anyone coming from an LDS background.
1.) The Pope doesn't mean the same thing to Catholics as the Prophet means to the LDS Church. On the surface they seem to be exactly the same thing, so it's easily misunderstood, but there are some important differences to be aware of.
2.) Catholic Doctrine and Dogma must be understood as being fluid. It can and will change drastically over time.
3.) There are varying interpretations within Catholicism that often will be opposite views on any given subject. Such disagreements are generally tolerated and sometimes even encouraged.
4.) Eclesiastical leaders disagreeing with the Pope on doctrinal matters is commonplace -- everyone remains respectful of his position, but they can and do completely disagree with him on certain matters both in belief and in practice. As long as the deviation from "official doctrine" is not too extreme, this sort of thing is simply tolerated. Within that framework, Archbishops and Cardinals disagreeing with the Pope on minor issues is commonplace. This is certainly not true of the LDS faith.
5.) The highest authority and ultimate word on any major change in doctrine or practice in the LDS faith would come directly from the Prophet. In the Catholic Church, the highest authority for significant change is an
Ecumenical council - Wikipedia, the free encyclopedia of Bishops -- I believe the minimum is 200 Bishops. While the Pope traditionally calls for such councils, they can be convened without his consent and he does not dictate what happens in them. The first Ecumenical Council was the
First Council of Nicaea - Wikipedia, the free encyclopedia. The most recent was the
Second Vatican Council - Wikipedia, the free encyclopedia is the most recent example of such a council.
6.) The Pope's authority needs to be understood as being location based -- he is the Bishop of Rome and as such is considered the direct successor to the Apostle Peter. Being the LDS prophet does not specify a location.
7.) As a result of number 6, the Pope is elected by a voting body of the eclesiastical leaders of the Holy See of Rome. Today they are known as Cardinals. The choice is said to be endorsed and validated directly by the Holy Spirit, but an LDS observer would probably find the process to be very politically driven. Naturally, that is simply a matter of perspective.
8.) The Pope is not an Apostle in the true sense of the word. The wording gets confusing here as Catholics refer to the line of Popes and "Apostolic Succession." The Catholic point of view, the 12 Apostles were never intended to continue on beyond the first century (or so) when the Apostles died out. The original 12 Apostles would be viewed as superior in authority to that of a Pope. The Papal Succession became the highest authority in the Church only after the last of them was dead. For an example, don't expect to see any new additions to the New Testament written by the Pope. The LDS Prophet, on the other hand, is viewed as Senior Apostle in every sense of the word. It would be perfectly acceptable for additional written revelation to be given to President Monson and according to the LDS point of view, that writing would be no less authoritative than the writings of Peter, James, John, Paul, etc.
9.) There have been some Popes in the past that have been absolutely despicable human beings.
Pope Alexander VI - Wikipedia, the free encyclopedia would be a specific example. They are still Popes despite their many misdeeds, and it is by no means a requirement for a Pope to necessarily be a good person. The modern Catholic would view this as an embarrassment to the Papacy that they will work dilligently to avoid repeating in the future. If an LDS Prophet were guilty of Alexander VI's list of sins and crimes, he would be excommunicated and replaced. The Papal succession, on the other hand, will just be seen as having survived a bad Pope. Modern circumstances of the Papacy have made the likelihood of another Alexander VI highly unlikely and Catholic leaders will no doubt be very dilligent to that end.