I have many Catholic friends, and I used to pray in a beautiful Catholic cathedral in Milwaukee, Wisconsin. I love Catholic people, and this is a critique of the salvation doctrine in their church, not a critique against the people.
My own church of origin, the Lutheran church, has similar problems with its salvation doctrine.
The main problem with the Roman Catholic Church is that it has a different ~way of salvation~ than Jesus and the Bible teach. The RC Church teaches, the same as every other false religion in the world, that our human-generated good works are what save us and will get us into Heaven.
The Bible clearly condemns this in the strongest possible terms in Galatians 1:6-9.
The Bible says that our ~good~ works are worthless to help our salvation.
The Bible teaches that salvation is a ~free gift~ that is received through faith in Jesus. John 6:47.