As you may know, m-mom, Orthodox and Oriental Orthodox Christians, who certainly take no back seat to the Latins when it comes to veneration of the Most Holy Theotokos, do not subscribe to the innovative and modern Latin Church dogma of the Immaculate Conception. This is a doctrine whose dogmatic status was declared by no Ecumenical Council but rather by a 19th century pope, not to fight a heresy as all the other real dogmas to that point were, but for other reasons apparently sufficient to him.
While no Orthodox Christian accepts this doctrine, some of us believe that it is positively heretical as a denial of the dual nature of Christ (True God and True Man)as declared by the 4th Ecumenical Council held at Chalcedon in 451 AD. If the Most Holy Theotokos was ontologically different from all the rest of mankind by being born without the tendencies to sinfulness we all carry as a result of the Sin of Adam, then she was not a human being, she was a "goddess" and her Son was not True Man.
This whole notion that she had to be "pure" or "without the stain (Macula) of Original Sin" is, it has been argued, driven by the fundamentally flawed Manichean notions of Blessed Augustine (whose Greek was not good at all and so he was cut off from the writings of the Greek Fathers) about "Original Sin". That whole concept is outside the consensus of The Fathers and is rejected by Eastern Christians, but this flawed doctrine probably lies at the base of the doctrine of the Immaculate Conception.
A number of the Fathers rejected this idea of the Immaculate Conception and some of the greatest theologians of the Latin Church did too. No less a figure than +Thomas Aquinas, the Angelic Doctor, denied it. It was essentially a doctrine developed by "Schoolmen" like Duns Scotus.
It is my understanding that many Protestants accept the Augustinian idea that man is utterly depraved. If so, then it stands to reason that such Protestants should immediately accept the Immaculate Conception doctrine since it strains credulity that God would be born out of depravity.
Once the West, including Protestants, accepted Blessed Augustine's non-patristic concept of Original Sin, all sorts of theological aberrations developed.
Gotta go shovel. We’re getting buried.
Later.....
Actually, in the very last section of Ineffabilis Deus, Blessed Pius IX wrote this about what he hoped for with his declaration of the dogma:
...[I]n her who is the most excellent glory, ornament, and impregnable stronghold of the holy Church; in her who has destroyed all heresies and snatched the faithful people and nations from all kinds of direst calamities; in her do we hope who has delivered us from so many threatening dangers. We have, therefore, a very certain hope and complete confidence that the most Blessed Virgin will ensure by her most powerful patronage that all difficulties be removed and all errors dissipated, so that our Holy Mother the Catholic Church may flourish daily more and more throughout all the nations and countries, and may reign "from sea to sea and from the river to the ends of the earth," and may enjoy genuine peace, tranquility and liberty. We are firm in our confidence that she will obtain pardon for the sinner, health for the sick, strength of heart for the weak, consolation for the afflicted, help for those in danger; that she will remove spiritual blindness from all who are in error, so that they may return to the path of truth and justice, and that here may be one flock and one shepherd.
So, in a sense, Blessed Pius was invoking her to fight all heresies.
It is my understanding that many Protestants accept the Augustinian idea that man is utterly depraved. If so, then it stands to reason that such Protestants should immediately accept the Immaculate Conception doctrine since it strains credulity that God would be born out of depravity.
The problem then occurs of how Mary was preserved free from the stain of original sin from her parents when she even had a human father. Whatever God could do to preserve HER from sin and have her immaculately conceived and sinless, He could do for Jesus without the necessity of her being sinless.
That's where the whole immaculate conception idea falls apart.
Since sin is inherited through the father, Jesus was free of that corruption, no matter how contaminated the world around Him was.
Sin is not greater than Jesus and that is, in effect, what Catholicism is inadvertently saying when they insist, even demand, that Mary have been sinless to keep Jesus sinless (or unstained or uncorrupted or however they want to put it).
It is my understanding that the main objection from Orthodoxy arises not from the idea that it means Mary is elevated to the status of goddess by the doctrine. (Which I have never come across in any readings about disagreements between Orthodox and Catholics on the doctrine). But from our Churches differing views on the doctrine of Original sin.
On original sin the CCC reads “Although it is proper to each individual,295 original sin does not have the character of a personal fault in any of Adam’s descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence”. Baptism, by imparting the life of Christ’s grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.”
This is in contrast to the Reformed doctrine of total depravity. If we did hold to a doctrine of total depravity than yes the IC would be necessary so that Jesus would not be tainted. But that is not the reasoning behind the Doctrine.
As for the Doctrine being declared late meaning it was a new teaching or belief history demonstrates otherwise. It had long been believed that BVM was free from personal sin. Several fathers suggest she was wholly without sin, personal or original. But that was not universally agreed upon. The question was if she was indeed “full of grace” how was she preserved from original sin? The debate between theologians attempted to give an answer to that question. The one thing that was agreed upon was that Mary needed Jesus to save her.