You know, myths don't pop out of nowhere. They have sources or inspirations. The Jesus myth was first written down, what, 2, 3, 4 generations after his supposed life and death? That is a lot of time to tell and re-tell stories by campfires, and a lot of time for those stories to grow and evolve and blend with different myths and stories that are told around those same night fires.
When I look at stories from the childhood of my father and his sister,
even the "epic" tales are told so differently by each of them. Something happened with either fire crackers or a makeshift rocket, and either the roof of my grandparents' garage, or perhaps the whole garage. Did my father attempt to build a rocket to the moon, and burn down the family's garage? Or was there an incident with firecrackers that put a hole in the garage ceiling? Or something completely different? Something happened. The story is told differently by different people.
I can't help but think that a man named Jesus lived and preached and collected a bunch of followers. The lack of any contemporary evidence of his existence seems to indicate that he was much less important in his lifetime than the current myths suggest. Lots of wandering preachers addressed the concerns of an oppressed and occupied populace. Lots of people were crucified. We certainly don't have records of most of them. The gospels are pretty unclear on dates. That is not inconsistent with an oral history. Was my dad 8 during the firecracker incident or 13 during the rocket incident? Even people who lived through and witnessed the events can't agree. So a few generations after the life of this preacher, folks carrying on an oral tradition would certainly be expected to have differing accounts.
I also suspect that a man named Noah saved himself and his family and a bunch of farm animals, against all odds, in a devastating flood. The story was told over and over, and little kids asked "why" and an angry god was given as an explanation for a flood that covered the entire world, and when those little kids grew up, they told their kids about the angry god, and when their kids asked about how all of the animals in the world survived, the storyteller explains that Noah took two of every animal in the whole world, (because god told him to) and instead of a raft, the vehicle morphs into an ark, and the next generation adds some new details and leaves out other details, but the story grows and grows.
I don't think that the Jesus myth came from nowhere. It might be a composite of various different charismatic preachers, who made a huge impact on a small set of contemporaries, but little impact on the larger society. And if those followers told the story over and over, and a generation later, travels arrived, having heard similar stories, and they combined the best aspects of both sets of stories, until everyone was convinced that the stories had been identical to begin with. The stories were embellished with parts of old myths that were told around different sets of camp fires, and miracles started to occur, and famous historical characters were incorporated, and the stories took on a life of their own, long before anyone decided to start writing them down.
Take a peek at the wiki article on mythology. Scroll down to the "Origins of Myths" section, and tell me which option seems the most likely explanation for the origin of the Jesus myth. http://en.wikipedia.org/wiki/Mythology