Prior to doing some research, my contention was that Catholicism was another true church of God. I answered Christian complaints of Catholicism with similar complaints of Christianity. I indicated that Catholics are extra-curricular, but so are Christians.
I did a little research. I was actually bias in that I was siding with Catholicism and hoping for some concrete biblical answers to support some of their practices. But my search yielded not a single acceptable answer.
Work Based Salvation I was under the impression that the Catholic tradition of 'confirmation' was a method of establishing the good habits of Catholicism. But as it turns out, Catholics believe that through their works in this life, and the 'purgatory' life, they will pay the debt of sin. It has become evident to me that Catholics have overlooked the central doctrine of their own religion. The debt of sin has already been paid. That is why Jesus came to earth. Why call Him a savior if you are saving yourself?
Purgatory I am fairly certain that this concept was invented to placate the parents of children who had perished before they were old enough to understand the Bible and truly accept Jesus. To such a parent, I can say only: take comfort! For Jesus said: "The kingdom of heaven belongs to people like these." Matthew 18:3 If the kingdom of heaven belongs to those who will accept it as a child would, purgatory for a child would not at all be necessary. Furthermore, the only evidence for purgatory that Catholics provide is the ongoing belief in purgatory. (Source) This seems derivative of the Islamic Qua'ran which states that it provides its' own authority. A common tactic of an untrue religion is putting a wall around your beliefs. Nobody can rebuke or confirm it.
Carved Images Exodus 20:1-5 blatantly states, "Do not render any carved images of heaven above." Catholicism says, "We did it anyway." Source
The Trinity (Also see article titled The Oneness Of God John 8:58 Jesus said "Before Abraham was, I Am." I think this statement alone confirms the oneness of God. But I will support this further anyway, just so there is no reasonable doubt. In many instances, Jesus is referred to as Gods' begotten Son. Begotten means that everything God is, Jesus is.
Other Worship of the virgin Mary and other saints are also practices based on themselves. In the first century AD, Catholicism contradicted the Bible. They continued to do it and basically said, "Well, it is how we have always done it. So it cannot be wrong." They are based on not even misinterpretations of the Bible, but clear, obvious, maybe even spiteful neglect of it! In one instance they say "Jesus was born by the seed of David and blessed by God," yet they continue to assert that Mary was a virgin for entire life, and worship her on this basis. I take three issues with this. 1) Mary had nothing to do with who Jesus is. All of the worship being directed toward her should be directed toward God. 2) Mary was not a virgin for her entire life. She had other children. 3) If Jesus was born of the seed of David, then the famed virgin birth is a normal birth.
A final note concerning Mary: Catholics will teach that she was freed from original sin. But she was not. Jesus was! Original sin is being tainted by the sin of conception. Mary was still tainted by the sin of her conception.
Catholics: I do not know what you think Jesus came to do. But your sins are immediately forgiven on the basis that you acknowledge them as sins. Rejoice, for your debt has already been paid.