In the movie "Zeitgeist", Peter Joseph says, "Justin Martyr, one of the first Christian historians and defenders, wrote: 'When we say that He, Jesus Christ, our teacher, was produced without sexual union, was crucified and died, and rose again, and ascended into Heaven we propound nothing different from what you believe regarding those who you esteem sons of Jupiter.' In a different writing, Justin Martyr said, 'He was born of a virgin, accept this in common with what you believe of Perseus.'"
There is a significant problem with mythicists taking this as an admission that the Jesus story was based on earlier mythology. If Justin Martyr was acknowledging that Jesus was a fictional character, then why did Justin Martyr continue to believe in Him?
Another is that if Justin Martyr was talking here about literal parallels, then why wouldn't the pagans he was writing to have already seen them for themselves?
Justin Martyr is not admitting to any literal parallels, but is trying to convince them that it's ridiculous to reject Jesus because He performed miracles when they believed their own deities performed miracles. If the pagans' deities really were produced asexually, crucified, died and rose again, then what would be the point of Justin saying all of this to them? What, they didn't already know? What Justin is saying is that the stories the pagans believe in are similar in miraculousness, not in exact details. He's saying that if the pagans reject Jesus because He was credited with miracles, then why do they continue to believe in the miracles credited to their deities?
Justin Martyr was clearly a Christian, yet Peter Joseph is suggesting that Justin knew that the Jesus story was a work of fiction based on the pagan stories, yet continued to believe in it anyway. How does this make any sense?