How in the world is it unholy for a married woman to give birth to children?
For your mother or mine, whose God-given vocation was to marriage and family life, it is its own holiness. But, are you really thinking this through? Jesus, through Whom all of creation was created (
John 1:1-4), being an eternal part of the Godhead, was involved in the ideation of Mary within the Divine intellect as part of God’s plan for creation and the salvation of mankind. As part of bringing this plan to fruition, He created Mary for the specific purpose of being His mother - He created her flesh so that she could in turn give that flesh to Him for the salvation of all mankind. This was fore-ordained from all eternity. The fulfillment of a vocation is a perfect conformity with the will of God. Inasmuch as God conceived of Mary for the sole purpose (vocation) of giving her flesh to the Christ, and of accompanying Him from virgin womb to virgin tomb, her vocation was Christ Himself. Her own son was her Lord and Master, her vocation, and the very reason for her existence. She existed only because of Christ, and was fulfilled only in Christ. The annunciation changed everything, forever.
To this end, we see in Luke’s Gospel that Mary vowed before Gabriel that she was the handmaid - even the bond slave - of the Lord. That same Lord would take flesh, in a way which she could not comprehend (nor can we, fully) as the baby which she would deliver to the world. Since her purpose was to give flesh to the Redeemer, her vocation was fulfilled only in conforming herself and her life to serve that vocation. Her Lord and Redeemer - her own Son - spoke the words to us to lead us to understanding of His mother’s vocation: 'Man cannot serve two masters." During her conversation with Gabriel, Mary chose her Master - both in this life and in eternity: her own Son. Her service was dedicated solely to God, in perfect conformance with His will and His intended vocation for her.
To break this vow which she made before Gabriel; to then disregard her vow before God and seek her own pleasure; to choose the satisfactions of this world over the reward provided by God, was unthinkable to her and, if you know Mary’s character, impossible. We cannot impose our 21st century western civilization concept of a “normal” family life upon the only woman in all of history and all of creation, who was predestined to bring about the redemption and salvation of all mankind. We are then thinking as man does and not as God does. Mary answers directly to God for everything. She was aware of this even before, and especially after her vow. She could (and would) serve no other. The difference with Mary is that she knew this, while you and I seek to avoid this knowledge.
If we take the earthy and simplistic view of a man and a woman who are married, we can see only the earthly pleasures of marital union and the “norma” family life. That is how the flesh thinks - carnally, sensually. But, neither your family nor mine could redeem mankind. Neither your family nor mine was conceived of before creation for that specific purpose. But, one unique family, out of all that would ever exist,
was. And, therein lies the difference.