Your wrong, the Catholic Church does teach Mary was born without sin. This is the problem with most so called Christians, they do not take the time to find out what a Church teaches before they join that Church.
We are to believe and accept ONLY that which the Holy Spirit teaches in the Scriptures. The Holy Spirit clearly has said all have sinned and clearly the Catholic Church teaches Mary was sinless.
Another thing is when Catholics confess their sins to a Catholic Priest it is mandatory for the forgiveness of their sins to pray the Hail Mary over and over and over again. They are praying to Mary, not to God.
I find it astounding so many people will not take the time to study the Scriptures and compare them to what certain Churches teach.
The vast majority of Catholics don't ''join'' the church, they are born into a Catholic family and are Christened as babies
they are then confirmed as members in later childhood which by that time have been indoctrinated into the Catholic view of Christianity. Apart from that family loyalty and Peer pressure has a huge influence on their beliefs and attitude towards those outside the Catholic faith. This is not peculiar to Catholics only. People born into Protestant denominations also
experience the same sort of process.