I believe where most of us Protestants would disagree is with Mary being described as "morally guiltless" and, of course, we would reference that "all have sinned and fall short...". I think Calvin (and Luther) was too close to the Catholic Church on this view coming directly out of Catholicism as he did. His arguments for Mary are a tad bit weak unlike many of his other doctrinal stances.
If memory serves me correctly, while tradition speaks of Mary being a perpetual virgin, I don't believe many of these documents came into being until several hundred of years after Christ and Mary. Her ascension (Catholic doctrine) wasn't talked about in writing until 5-6 AD. While Mary was undeniably a great woman of God and IS blessed, in my mind it is a romantic notion to believe that she was morally guiltless. None of this is supported by the inspired writings of God's word and there are plenty of other scriptures that state otherwise.
However, I will say that while I disagree with you theology, you Orthodox are more consistent with your theological views than the Catholics, IMHO. I appreciate well reasoned theology even if I disagree with the conclusion.
BTW and FWIW-It is my particular view that all women wombs are holy and pure. Mary, outside of her humbleness and dedication to God which is NOT to be minimized, was physically no different than any other woman. Original sin is transmitted through the male, who is corrupt. Consequently any woman could have been chosen as a vessel of an incorruptible seed. The issue isn't the vessel as much as the seed which required a virgin birth.
If memory serves me correctly, while tradition speaks of Mary being a perpetual virgin, I don't believe many of these documents came into being until several hundred of years after Christ and Mary.Your memory is mostly right. The earliest surviving text documenting the tradition of Mary's perpetual virginity seems to be the apocryphal Protoevangelum of James, ca 120 AD. Origen's Commentary on Matthew, ca 248 AD, is another surviving early text speaking of Mary's perpetual virginity. Many more texts survive from the fourth and fifth centuries, written by people like St. Augustine.