In the introduction to "Who Needs Christmas," Andy Stanley said one of the challenging things about the Christmas story is the story itself, because there's so much miraculous, so much that's unbelievable about it. The thought may be, Hey, they had to come up with some myth about the birth of Jesus to give him street cred. But if somebody can predict their own death and then their own resurrection, I’m not all that concerned about how they got into the world. Christianity doesn’t hinge on the truth or even the stories around the birth of Jesus.
i) There's nothing wrong with verbalizing doubts or objections that people may have, as a preliminary step to knocking them down. But having been raised, they can't be disposed of in such a perfunctory way.
None of us heard Jesus predict his death and resurrection ahead of time. Rather, we have accounts that were written after the fact. Unless, therefore, these accounts are trustworthy apart from his predictions, an unbeliever can simply dismiss Andy's appeal as "prophecy" after the fact. An unbeliever can say there's no reliable evidence that Jesus actually said these things before they happened, since we don't have any records that predate the reputed predictions.
ii) And, of course, if the nativity accounts are pious fiction, then that raises questions about the historicity of Matthew and Luke generally. If that's mythical, why not other miracles attributed to Jesus–up to and including the Resurrection? In that event, are the Gospels historical or hagiographical?
iii) Furthermore, predicting your own death can be a self-fulfilling prophecy if you goad the authorities into killing you. So, once again, a skeptic will be unimpressed–even if Jesus did predict it.
iii) If two canonical Gospels narrate how Jesus was born, who does Andy think he is to tell people that the truth of Christianity doesn't hinge on the veracity of those accounts? That would mean God misled all Christians by allowing fictonal stories about the birth of Christ to creep into the Gospels.
iv) What does it even mean to say that Christianity doesn't hinge on the truth of Gospel "stories" about how Jesus got into the world? The point of the "stories" is that how he got into the world tells us who or what got into the world. It's the "story" of a person who came into the world from another world (heaven). He preexisted our world. Indeed, he made our world. He didn't originate at the moment of conception. Humanly speaking, Jesus came into being at the moment of conception, but there's a dimension to Jesus that never came into being: the divine Son of God.
v) Moreover, the nativity stories tell us other important things, like why he came into the world: his mission. Likewise, they describe his birth as the fulfillment of prophecy. It's a theological introduction. That's not something you can just lop off, leaving everything else intact.