This post indicates that the author may have been raised a Catholic, but he didn’t understand the doctrine of the Immaculate Conception. Mary was given the grace of being born without original sin so she could be a worthy mother to our Lord. This Grace was given in anticipation of the saving act of the Sacrifice on the Cross. Her prayer after the Annunciation, the Magnificat, specifically pronounces this in the beginning:
My soul proclaims the greatness of the Lord
My spirit rejoices in God my Savior.
The reason Jesus had to be born of a virgin is because he would have inherited Adam’s sin if he had a biological father. Somehow Mary was able to be without the taint of original sin with a biological father but Jesus was not if we believe Catholic theology.
Her prayer pronounces that she was without sin?
BTW, the Immaculate Conception is a fairly recent addition to Catholic doctrine.