There is more than one problem that comes to mind when considering the virgin birth.
They are primarily in relation to Joseph
Some time after the conception of Jesus, Joseph married Mary, and was to continue as her husband for many years.
Jesus was conceived of an unmarried woman.....This would be considered sinful by most Jews and Christians, even today.
The marriage to Joseph regularised the position in the public view.
However the conception would still have been thought sinful between any three other people, as it was outside marriage.
There is no mention, or inference, in the Bible that the marriage between Mary and Joseph was nominal or purely platonic. In fact it would be thought highly unusual for such a marriage to survive. There are several mentions of Jesus Brothers and there is no evidence that these are other than the sons of Mary, fathered by Joseph.
The Catholic Church takes a wholly unrealistic view, that Mary was and remained a Virgin.
I think it does so to avoid discussion on any of the above. And to remove any hint of a sex act by Mary. This conforms to their view that sex is sinful and is only mitigated by conception in marriage.
This is reinforced by the belief in the sinful and carnal nature of Eve, allied to belief in original sin.
To remove the status of Mary, as a perpetual virgin, seriously undermines the Catholic views about the sinful nature of sex.
It is difficult to explain why God placed Mary in the sinful position of becoming an unmarried mother. . . That she was betrothed to Joseph hardly improves the situation.
