N.T. Wright addresses the “modern” realization that virgin birth cannot happen and the deeper reasons for why so many reject the teaching:

“Let’s get rid of any idea that we now know that virgin births don’t happen because we know about modern genetic science. Actually, people two thousand years ago were not ignorant. As C. S. Lewis once tartly pointed out, the reason Joseph was worried about Mary’s pregnancy was not because he didn’t know where babies came from but because he did.

“It was fascinating, in a classic moment of misreporting a few days ago, that when the Archbishop of Canterbury pointed out that Matthew doesn’t say how many Magi there were people thought he was a heretic, but when he said he really did believe in the virginal conception of Jesus nobody noticed.

“Actually, the strange story of Jesus’ being conceived without a human father is so peculiar, particularly within Judaism, and so obviously open to sneering accusations on the one hand and the charge that the Christians were simply aping the pagans on the other, that it would be very unlikely for someone to invent it so early in the Christian movement as Matthew and Luke. But there’s more to it than just that. The virginal conception speaks powerfully of new creation, something fresh happening within the old world, beyond the reach and dreams of the possibilities we currently know. And if we believe that the God we’re talking about is the creator of the world, who longs to rescue the world from its corruption and decay, then an act of real new creation, anticipating in fact the great moment of Easter itself, might just be what we should expect, however tremblingly, if and when this God decides to act to bring this new creation about. The ordinary means of procreation is one of the ways, deep down, in which we laugh in the face of death. Mary’s conception of Jesus has no need of that manoeuver. ‘In him was life, and the life was the light of all people.’ The real objection to the virginal conception is not primarily scientific. It is deeper than that. It is the notion that a new world really might be starting up within the midst of the old, leaving us with the stark choice of birth or death; leaving us, like the Magi, no longer at ease: leaving us, in other words, as Christmas people faced with the Herods of the world.”

From a sermon titled “Power to Become Children: Isaiah 52.7-10; John 1.1-18”. See the full transcript here.