From a practical if not an historically empirical standpoint, most myths whether explanatory or descriptive, function as a heuristic device to lure novices to a desired manner or thinking. Needless to say, all myths are fictitious. This is fine as long as the progenitors of the myth don't try to sell the myth as truth. When religious myths are sold as truth, problems can ensue.
Religious myths should function exactly like training wheels on a bicycle: the training wheels aid the child/novice-rider in learning to ride a bike. When the bike can be balanced, and hence successfully ridden, the training wheels are discarded and forgotten. They have served their purpose. Similarly, religious myths exist only to facilitate indoctrination into a religion. Once acceptance of the religion is achieved, these myths should be abandoned. Any religion based solely on myth qua truth is only embraced by the puerile, and herein lies the danger:
In 325 A.D. at the first council of Nicea, men voted to adopt Athanasius' - a Greek bigwig who later was promoted to Bishop of Alexandria - doctrine of homoiousianism. This doctrine declares that Jesus was co-substantive with God the Father, that is, Jesus wasn't exactly God the Father, but similar.
A safe bet says this is about the time Christians started using the term for Jesus: 'Son of God' - not exactly God but similar. Given that, it can't be much later that the myth, "Jesus' mommy was a virgin" came about, and was taken as absolutely true. "Hook, line and sinker" comes to mind.
Myths - only created by men - taken as true by the puerile can be used as a very dangerous means to a very bloody end. The majority of the bloody history of the world is defined by and explained thru religious true-believers and political true-believers, and as the succinctly descriptive term Nietzsche coined puts it: eternal reccurrence.
Maybe, in the end, we all will become victims of the myth lab.