"While...
...Mary's SinFULness has to do with the Bible verse:
Romans 3:23
...for all have sinned and fall short of the glory of God,..."
True, I've heard that argument before, but if one took that verse to be all inclusive of all humans it would also include Christ, children who died before having the necessary faculty to sin, as well as Mary. One could argue that Jesus was exempt because He was God, and that young children still have original sin. I myself follow the Church's teaching that a special exception was made for Mary the mother of Jesus. And that the Grace of his sacrifice was applied to her in order that she might be free from sin.
It ultimately comes down to interpretation either way. I'm a Catholic. I believe the Catholic Church through it's Magisterium (The pope and the bishops in communion with the pope) have that authority when it comes to matters of Faith and Morals. Others do not.
Some of the Church's teachings seem hard, but what I've found is that they actually make more sense than what I personally thought. I just wanted to A) be able to judge for myself, and B) have it fit into my modern 21st century way of thinking. With age and experience I've found out how wrong that way of thinking can be.
Just WHEN did this 'teaching' begin in the Catholic Church?