It is true (as piq writes) that the word often translated in the Bible as "virgin" could have been intended to mean simply "young woman." But the Catholic Church (and many Protestants who attest to Mary's perpetual virginity) do not disregard this.

An aside: The Catholic Church is not respectfully called the Roman Catholic Church, because it consists of the churches under the Patriarchy of Rome, and about 23 churches under Eastern Patriarchs who follow the Pope. The Roman Catholic Church and the Eastern Catholic Churches together make up one communion with the same doctrine, called the Catholic Church

The reasons the Catholic Church and many other Christians assert the virginity of Mary:

  • In the Gospel of Luke, the Angel Gabriel tells Mary she will give birth to a son, and she asks how this is possible since she has never had sexual relations. The Angel explains that the Holy Spirit will come upon her, and therefore the son will be holy, the Son of God (Luke 1:31-35).
  • Also in Luke, Gabriel tells Mary she is "full of grace," and that the Lord is with her, and Elizabeth tells Mary she is "blessed among women." This implies her special status in the eyes of the Lord, and suggests that she would choose the more noble path of virginity over consumated marriage. (Luke 1:28,42).
  • Matthew explains that Mary was found unexpectedly with child when she was betrothed to Joseph. Joseph, being righteous, decides to quietly divorce her, when the Angel tells him of the child's divine origin and so he marries her and becomes Jesus' adoptive father.
Besides scriptural justifications, Christian tradition has always supported the virginity of Mary:
  • Mary was immaculately conceived, and throughout her life was sinless, and so she must have been a virgin. Marriage and sex are not sinful per se, but they are not as holy a life as serving the Lord as virgin, especially if you are serving your Son, Jesus.
  • Christian tradition has also explicitly maintained Mary's virginity.
  • The Church, asides from scripture, joyfully incorporates Sacred Tradition into her doctrine.

So nothing was "disregarded." Saying Mary was a "young woman" does not mean she was not a virgin.

In response to Dreamvirus:

  1. Isaiah prophesizes that the young woman (which can but does not necessarily mean "virgin") conceiving will be a sign! Not just any sign, but a sign of the Messiah! What kind of sign of would be a woman conceiving be? Happens all the time! It had to be something miraculous, maybe because she would have 100 children, or because the child would be a dragon, etc. Using Occam's Razor and common sense, I feel safe interpreting the prophesy as predicting that a virgin shall conceive.
  2. From the Christian point of view, the Gospels were written from the actual life of Christ, and the reason this allies with Isaiah is because Isaiah was inspired by God! Of course I understand the secular view that the Gospels were deliberately composed to fulfill the Isaiah prophecies (I used to hold it), but the idea that the authors simply wrote what they believed is also reasonable.
  3. "The mistranslation in Isaiah prompted the authors of some of the Gospels to add further legitimacy to Jesus' status as the Messiah by stating that his mother was a virgin." -- The idea that Jesus was born of a Virgin was ridiculed and was not a method of legitimizing Christianity in the early church. Later on in Christian history the beauty of Mary's role has been elaborated, but the idea that writing about Mary's virginity back then brought anything but scorn is false. Some evidence of this can be seen in the writings of non-Christian historians of the time, especially Josephus.