Cult: a religion regarded as unorthodox or spurious (Merriam Webster's online dictionary).
Spurious: outwardly similar or corresponding to something without having its genuine qualities : FALSE (Merriam Websters online dictionary)
The Catholic Church has a history of teaching heresy, and still teaches heresy, about the Pope, fasting, church authority, and church history and many foundational beliefs about Christianity.
For starters, the Catholic Church believes and teaches that the Pope is the head of the church.
As the Catholic Apologist website Catholic.com explains:
We have shown in the last section that Christ conferred upon St. Peter the office of chief pastor, and that the permanence of that office is essential to the very being of the Church. It must now be established that it belongs of right to the Roman See. The proof will fall into two parts: (I) that St. Peter was Bishop of Rome, and (2) that those who succeed him in that see succeed him also in the supreme headship. [1]
This has major Scriptural problems for clear reasons, mainly:
"For the husband is the head of the wife, as Christ also is the head of the church, He Himself being the Savior of the body." - Ephesians 5:23
He is also head of the body, the church; and He is the beginning, the firstborn from the dead, so that He Himself will come to have first place in everything. - Colossians 1:18
"and in Him you have been made complete, and He is the head over all rule and authority;" - Colossians 2:20
But they also inaccurately claim that Peter is the foundation of the church:
The word for Peter and for rock in the original Aramaic is one and the same (N~D); this renders it evident that the various attempts to explain the term “rock” as having reference not to Peter himself but to something else are misinterpretations. It is Peter who is the rock of the Church.[1]
There's one problem with this... Peter himself never even claimed this about his position in the church:
4And coming to Him as to a living stone which has been rejected by people, but is choice and precious in the sight of God, 5you also, as living stones, are being built up as a spiritual house for a holy priesthood, to offer spiritual sacrifices that are acceptable to God through Jesus Christ. 6For this is contained in Scripture:“BEHOLD, I AM LAYING IN ZION A CHOICE STONE, A PRECIOUS CORNERSTONE,AND THE ONE WHO BELIEVES IN HIM WILL NOT BE PUT TO SHAME.” 7This precious value, then, is for you who believe; but for unbelievers,“A STONE WHICH THE BUILDERS REJECTED,THIS BECAME THE CHIEF CORNERSTONE,” 8and,“A STONE OF STUMBLING AND A ROCK OF OFFENSE”; - 1 Peter 2:4-7
Here Peter himself calls Christ the cornerstone of the church. If Peter believed he was the foundation of the church, then why call Jesus the cornerstone? It is because Peter knew that Jesus, not himself, was the foundation of the church.
Moreover, Paul also calls Jesus the foundation of the church:
10According to the grace of God which was given to me, like a wise master builder I laid a foundation, and another is building on it. But each person must be careful how he builds on it. 11For no one can lay a foundation other than the one which is laid, which is Jesus Christ. - 1 Corinthians 3:10-11
So both Peter and Paul agreed that Jesus, not Peter, was the foundation of the church. This, therefore, means the Catholic Church believes heresy about Papal supremacy and Peter's divine placement as the foundation of the church.
But not only do they err in papal supremacy, they also do not adhere to church tradition regarding sola scriptura.
Catholic.com explains:
A Catholic would not use the term sola scriptura—which is historically contentious and highly prone to misunderstanding—but he certainly can agree that the basic facts of the gospel and how to respond to it can be derived from Scripture. A Catholic would add that these facts need to be understood in the light of Sacred Tradition and that the Church’s intervention may be necessary to make sure they are understood correctly.[2]
Here, again, Catholics invent their own doctrine that simply was not to be found when Christianity was founded.
In Against Heresies, a work that Catholics have extremely high regard for, Irenaeus, who was an actual student of a pupil of John the Apostle, says that the Scriptures are the ultimate authority for doctrinal matters:
Suppose there arise a dispute relative to some important question among us, should we not have recourse to the most ancient Churches with which the apostles held constant intercourse, and learn from them what is certain and clear in regard to the present question? For how should it be if the apostles themselves had not left us writings? Would it not be necessary, [in that case,] to follow the course of the tradition which they handed down to those to whom they did commit the Churches? - Against Heresies, Book 3, Chapter 4 paragraph 1
So in the case of disputes, Irenaeus makes it clear that the early church sought THE WRITINGS OF THE APOSTLES to settle them before any sort of oral tradition. They didn't rely on oral tradition to interpret these writings. They went to the writings themselves and interpreted them on their own merit.
This is a fact that is also confirmed by Clement of Rome, who lived at the same time as the Apostles. Catholics also believe he is the second Pope after Peter:
The apostles have preached the Gospel to us from the Lord Jesus Christ; Jesus Christ [has done so] from God. Christ therefore was sent forth by God, and the apostles by Christ. Both these appointments, then, were made in an orderly way, according to the will of God. Having therefore received their orders, and being fully assured by the resurrection of our Lord Jesus Christ, and established in the word of God, with full assurance of the Holy Ghost, they went forth proclaiming that the kingdom of God was at hand. And thus preaching through countries and cities, they appointed the first-fruits [of their labours], having first proved them by the Spirit, to be bishops and deacons of those who should afterwards believe. Nor was this any new thing, since indeed many ages before it was written concerning bishops and deacons. For thus saith the Scripture in a certain place, “I will appoint their bishops in righteousness, and their deacons in faith.” - Epistle To The Corinthians, Chapter 42
So here Clement states that the order of authority in the church is first God, then the Apostles, and THEN the deacons and bishops. So it follows from this that the writings of the Apostles, by the Apostles' very nature of superceding those left after them, supercedes the teachings of those who followed them.
This is why Irenaeus says that the church first consults the writings of the Apostles when controversy strikes. So the concept of Sola Scriptura is actually the true tradition.
Catholics also teach many other peculiar beliefs such as prayer to the saints, abstaining from meat, and other false doctrines that are not to be found anywhere in the early Christian writings as proper doctrine.
Therefore, the Catholic Church is a cult.
SOURCES: