The idea that the Genesis account of the Creation of the Universe and the Fall of Humankind is a myth is not new to the Church. I remember being surprised when my Episcopal priest told me that he thought the earliest historical person in the Bible was Noah. This would imply that he, too, thought the Genesis account was not historical, but rather, a myth. No doubt he believed, as I now do, that the myth carries a true message for us, despite its lack of historical truth.
But taking Genesis 1-3 as myth deconstructs the standard Christology (the theology of who Christ is, the reasons for the Incarnation, Crucifixion, and Resurrection, and their implications for all of us). The standard Christology is that of the Apostle Paul and St. Augustine, namely that God created the primordial couple (Adam and Eve) in a state of Grace, in which there was no suffering or death, and no need to labor to survive. Through disobedience to God's only prohibition - to refrain from eating the fruit of the Tree of Knowledge of Good and Evil, Adam and Eve incurred God's punishment - they would have to labor for their food, clothing and shelter, childbirth would be painful, and suffering and death entered the world - for them and all their descendants, including us. In order to rescue us from this situation - in order that death not be final - God became incarnate as a fertilized human ovum in the womb of the Virgin Mary. The ovum grew to become the baby, and eventually the man Jesus, who lived a blameless life, and suffered death by crucifixion. On the third day after his death, he arose to a new life, met with many of his former followers, and then ascended to Heaven to "sit on the right hand of God." The reason for this drama, is that Jesus thus paid the price of the primordial disobedience for all of humanity (or at least all of humanity who would believe it and thank him for it). The effect of having this price paid, is that after death we will be blameless before God - our sins will be forgiven - and we, too, will be resurrected to new life with God. Jesus is the first of the resurrected, and will draw us after him.
Now if Genesis 1-3 is a myth, (which many thoughtful people find repulsive - God the Abusive Parent, they call it) where does that leave Christology? One can reconstruct Christology based on the Crucifixion itself, or one can simply use 20th Century history as prima facie evidence of humanity's sinful nature. Either way or both ways, one gets a Christology that is consistent, and consonant with (even faithful to) the original.
But for many people, it just isn't as compelling. Maybe that's why the mainline Protestant churches are declining in membership, while the so-called "Evangelical" churches are growing. People need for there to be magic in the world. People need their mythology to be their history. Maybe the church that grows is the church that does the best job of selling its fairy-tales.
Perhaps that last jab was too bitter. It just bugs me when churches mix God's Truth with obvious falsehood, and tell me that I have to swallow the whole package to be a real Christian.