First, you assert that the authority the Catholic Church has, it gave to itself. I would argue that Jesus Christ gave the apostles the authority to teach the word of God:
Then Jesus approached and said to them, "All power in heaven and on earth has been given to me. Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, until the end of the age." (Mt 28:18-20)"Whoever receives you receives me, and whoever receives me receives the one who sent me." (Mt 10:40)
Do we agree that Jesus gave his disciples, the Apostles, the command to go out and spread the word of God, to "teach" the commandments? To share the "good news"? I think we do.
Catholics believe that Jesus made his Church on earth and put Peter, his apostle, as the head of the Church.
"And so I say to you, you are 'Rock', and upon this rock I will build my church, and the gates of the netherworld shall not prevail against it. I will give you the keys to the kingdom of heaven. Whatever you bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven." (Mt 16:18-19)"If he refuses to listen to them (two or three witnesses), tell the church. If he refuses to listen even to the church, then treat him as you would a Gentile or a tax collector." (Mt 18:17)
Jesus distinctly gives Peter the command to tend to his flock, the people:
When they had finished breakfast, Jesus said to Simon Peter, "Simon, son of John, do you love me more than these?" He said to him, "Yes, Lord, you know that I love you." He said to him, "Feed my lambs." He then said to him a second time, "Simon, son of John, do you love me?" He said to him, "Yes, Lord, you know that I love you." He said to him, "Tend my sheep." He said to him the third time, "Simon, son of John, do you love me?" Peter was distressed that he had said to him a third time, "Do you love me?" and he said to him, "Lord, you know everything; you know that I love you." (Jesus) said to him, "Feed my sheep." (Jn 21:15-17)After St. Peter, the first Pope, there is a clear line of succession. Not all Pope's were good men; indeed, some Pope's led very sinful lives. But the church itself is holy: Jesus said there would be both good and bad members in the Church (John 6:70), and not all the members would go to heaven (Matt. 7:21–23). But it's important to note that not one iota of doctine has been changed: the bad Pope's had no role in saying that Christianity meant anything other than what it meant since the time of Christ.Keep watch over yourselves and over the whole flock of which the holy Spirit has appointed you overseers (episcopous), in which you tend the church of God that he acquired with his own blood. (Acts 20:28)
I hope that you read why I wrote with an open heart, and think about it. I'm not trying to convert you, but to show you that the Catholic Church IS scripturally based, and that we hold fast TO scripture as the inspired word of God. That everything we do, and all our prayers, are directed to the Father, the Son and the Holy Spirit, the Holy Trinity that all Christians -- Catholic and non-Catholic -- believe in.
God bless.