this just in wrote:
I don't think it's special pleading because I'm not skeptical of the existence of Mohammad, for example. The existence of Mohammad (to me, at least) seems to be the simplest explanation for the rise of Islam.
Personally, I think that early Christians were far more influenced by Jewish sources, not Greco-Roman sources. New Testament writers seem much more concerned to show Jesus patterned after Jewish heroes like Moses, Elijah, or Elisha or fulfilling aspects of Jewish expectation than trying to incorporate hellenistic sources.
I don't think it is the simplest explanation, given the history of religion.
So do you think every religion that ever got popular had a historical founder? Osiris? Mithras? Zoroaster? We know Joseph Smith was a real character, but was Moroni (the angel who allegedly revealed the gold plates to Smith). Hey, lots of people, smart people, believe it and it is written in a book, so it must be true!
Read an extended discourse on the mythicist argument and the lines of evidence for Jesus (Robert Price, Earl Doherty, The Dutch Radicals, etc.) and for that of Mohammed (Ibn Wariq, working under a false name, explored this topic) and see how they answer this "simplest explanation" argument. I have read tons of both arguments and I am pretty compelled by the mythicist argument. I wouldn't want to bet money, but if I had to, I would bet it on mythicism.