Why the "Virgin Birth" is a fable?

There are at least a few dozen instances of virgin births in history that I'm aware of, mostly of religious figures.

Eighteen hundred years before Christ, we find carved on one of the walls of the great temple of Luxor a picture of the annunciation, conception and birth of King Amunothph III, an almost exact copy of the annunciation, conception and birth of the Christian God.

Roman/Greek: Demeter and Persephone, Rhea and Zeus, Apollo

In Egypt, virgin mother Isis begat Horus

In Phrygia, Attis was born of the virgin Nama.

A nymph bathing in a river in China is touched by a lotus plant, and the divine Fohi is born.

In Siam, a wandering sunbeam caresses a girl in her teens, and the great and wonderful deliverer, Codom, is born.

In the life of Buddha we read that he descended on his mother Maya, "in likeness as the heavenly queen, and entered her womb," and was born from her right side, to save the world."

In Greece, the young god Apollo visits a fair maid of Athens, and a Plato is ushered into the world.

From Greece comes the virgin birth of Adonis, who was resurrected after being killed by a wild boar. Adonis was revered by the Phoenicians as a dying-and-rising god, and Athenians held Adonia, a yearly festival representing his death and resurrection, in midsummer.

From the Americas comes a remarkable story of the god-man Quetzalcoatl told by the Aztecs and Mayans. Not only did he have a virgin birth, but he was associated with the planet Venus, the morning star, as was Jesus. In addition, the religion built around him used the cross as a symbolic representation. Like the myths around Jesus, Quetzalcoatl said he would return to claim his earthly kingdom.

Mithra was a Persian god who was also a virgin birth, but was more than just a tribal god. Mithra was born in a cave and had twelve companions. Mithra's birthday was also on December 25th. Both religions celebrate the resurrection at Easter. Much of what we know about Mithracism today came from the Christians. The prophet Zoroaster was also born of a virgin.

Perseus and Hercules all experienced virgin births after being fathered by yet other gods. Horus, Mithra, Dionysus and Krishna were all born on December 25th., their births were announced by "stars", attended by 'wise men', involved humble birth locations, entailed the massacre of innocents and fleeing for safety from enemies, and so on and on.

A Roman savior Quirrnus was born of a virgin.

In Tibet, Indra was born of a virgin. He ascended into heaven after death.

In India, the god Krishna was born of the virgin Devaki.

Virgin births were claimed for many Egyptian pharaohs, Greek emperors and for Alexander the Great of Greece.

For a discussion of several aspects of the Christian virgin-birth story, including speculation on origins.
http://www.religioustolerance.org/virgin…

Not only the idea of a virgin mother, but all the other miraculous events, such as the stable cradle, the guiding star, the massacre of the children, the flight to Egypt, and the resurrection and bodily ascension toward the clouds, have not only been borrowed, but are even scarcely altered in the New Testament story of Jesus.

http://www.sonn.com/~perly/glk/files/Mai…
Comparisons of the story of Jesus Christ to stories of other religious figures

http://www.church-of-chaos.de/literature…
http://www.sonn.com/~perly/glk/files/Uns…
http://www.uc.summit.nj.uua.org/Sermons/…
http://www.crosscircle.com/CH_2m.htm

http://members.aol.com/tjzee/iss174.htm
A discussion of the virgin-birth story from a modern perspective

Apparently virgin births were quite common up until the advancement of medicine and science. How would you explain it??