To argue against Mary’s perpetual virginity is to suggest something else that is greatly implausible, not to say unthinkable: that neither Mary nor her protector, Joseph, would have deemed it inappropriate to have sexual relations after the birth of God in the flesh. Leaving aside for a moment the complete uniqueness of the Incarnation of the Second Person of the Trinity, recall that it was the practice for devout Jews in the ancient world to refrain from sexual activity following any great manifestation of the Holy Spirit…
Mary became the vessel for the Lord of Glory Himself, and bore in the flesh Him whom heaven and earth cannot contain. Would this not have been grounds to consider her life, including her body, as consecrated to God and God alone? Or it more plausible that she would shrug it all off and get on with keeping house in the usual fashion?..
And then there is Joseph’s character to consider. Surely his wife’s miraculous conception and birthgiving (confirmed by the angel in dream-visions) and the sight of God incarnate in the face of the child Christ would have been enough to convince him that his marriage was set apart from the norm… If touching the ark of the covenant had cost Uzzah his life, and if even the scrolls containing the Law, the Psalms, and the Prophets were venerated, certainly Joseph, man of God that he was, would neither have dared nor desired to approach Mary, the chosen of Israel, the throne of God, to request his ‘conjugal rights’!