Why Does Mary Have To Be a Virgin?

We went to Mass yesterday. It was the vigil Mass for Christmas. Anyway this time of year, like no other, there is heavy emphasis on the virginity of Mary the mother of Jesus and I ask myself; why does this have to be?

If I point you to some internet-based information from the BBC then this is about the only page you will find on this subject, from a Google search, which is not apparently written by a bunch of ranting lunatics. On the BBC site you will find the following:-

The Gospels of Mark and John and the letters of St Paul do not mention the Virgin Birth. It is only included in the later Gospels of Matthew and Luke, although both give very different accounts. Professor James
Charlesworth says: "Should we take it literally, symbolically or metaphorically? Christians lineup behind every one of those".

If Mary’s pregnancy was not divine, who might have been the father of her child? As an unmarried mother-to-be, Mary was in a perilous position – Joseph could have had her banished or even stoned to death. But, according to the New Testament, Joseph was a good man and he did not abandon his young fiancée.

Historians have looked for reasons to explain Joseph’s loyalty and sympathy towards Mary. One second-century historian claimed that Mary was actually the victim of a rape by a Roman soldier called Panthera and, indeed, many women at the time would have been raped by soldiers. However, that story is much more likely to have been circulated falsely in an attempt to discredit the growing Christian movement.

Biblical historian Mark Goodacre concludes: "The Christian in me wants to say that it is quite likely to be God because I like the idea of a wonderful, miraculous birth – something supernatural … happening right there at the origins of Christianity. The historian in me does have some problems with that and does wonder
if Joseph is the better option."

Now the above is quite rational and does not try to come to any forced conclusion. So why does the Catholic Church insist that Mary was a virgin? Take this extract from the Catholic Catechism:-

People are sometimes troubled by the silence of St. Mark's Gospel and the New Testament Epistles about Jesus' virginal conception. Some might wonder if we were merely dealing with legends or theological constructs not claiming to be history. To this we must respond: Faith in the virginal conception of Jesus met with the lively opposition, mockery or incomprehension of non-believers, Jews and pagans alike; so it could hardly have been motivated by pagan mythology or by some adaptation to the ideas of the age. The meaning of this event is accessible only to faith (my italics), which understands in it the "connection of these mysteries with one another" in the totality of Christ's mysteries, from his Incarnation to his Passover.

It seems a little forced to me, and it goes on:-

Through the centuries the Church has become ever more aware that Mary, "full of grace" through God, was redeemed from the moment of her conception. That is what the dogma of the Immaculate Conception confesses, as Pope Pius IX proclaimed in 1854:
The most Blessed Virgin Mary was, from the first moment of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Savior of the human race, preserved immune from all stain of original sin.

Again, is this not a contrivance. "Through the centuries the Church has become ever more aware..." It's balderdash! It is either evident or it isn't. If it was not then fair enough. I personally do not believe that the story of Christ has to depend on the fact or otherwise of the Immaculate Conception. His teachings do not depend upon it. So why construct this legend, this myth. What purpose does it serve? Let me say right here that I have not (yet) read The Da Vinci Code. I haven't had time but I believe it fleshes out the argument that the whole issue of the Immaculate Conception is a vast conspiracy in order to cement the concept of male superiority in the Church and thus in society. You can let me know.

My basic problem is that I don't believe in the virgin birth, and I want to know why I should have to. Is there anybody of rational mind out there who can answer my question without saying "It's a mystery"?