So there is no chance whatsoever that the writers of the New Testament were influenced by any of the religions and traditions that came before?
Influenced is different than the plagiarism theory pulled out by Zeitgeist conspiracy theories. The "Wow! Cool! He just walked away from the explosion without looking at it! Let's write something similar in every action film ever made. That's so badass!" is what I'd call influence -- like how ideas from pagan festivals were christianized to form Christmas. I don't think anyone's mouth would drop if some of the parables or miracles were borrowed from other traditions. Illiterate people who don't travel much can unintentionally change details quite easily, as any modern game of 'Telephone' would prove. But completely fabricating Jesus from agricultural fertility deities is a bit of a different story.
How has it been debunked by the way? Without knowing the mind of the writers, surely it would be impossible to tell.
Most of the claims of the movie and the companion materials make very specific claims of what was plagiarized that can be proven to be out right lies (Krishna was a shepherd that was crucified), taken out of context (basically every "god-man" argument, everything with Osiris), based on linguistic fallacy (son=sun) or so vague as to be useless ("Miracles were preformed"wink