Firstly, the Catholic church is copying the Levitical priests who were mediators between the people and God. They are also copying the pagan priests who were mediators between the people and their pagan gods.
When Jesus ascended to heaven to intercede for believers, He because our great High Priest, the sole mediator between God and man. This abolished all priesthoods. Therefore, using a priest is denying that Jesus is our sole mediator between God and man, and if Jesus in denied in this way, He is no longer effective for those who use priests to mediate between them and God. And because Jesus is the sole "parachute" for salvation and salvation can come by no other, then those who use priests put their own salvation at risk.
Ministers of the gospel are there to preach the gospel and encourage the unsaved to receive Christ as Saviour, and to teach the Scriptures and disciple those to whom he is responsible in his church. He is not there to stand between the members and Christ, but to stand with them as they approach Christ for themselves.
As for me, I confess my sins to the only Person who can forgive them - God alone. Even the Pharisees said that only God can forgive sins. So if one goes to a priest confessing sin and gaining the priest's absolution for them, there is no guarantee that although they may be forgiven as far as the Catholic church is concerned, but not from God Himself.