That is a large topic that I could write a book on. Just to give you a few things, the first would be the amount of human ignorance found throughout the bible, literally starting from page 1. If I cannot suspect an advanced alien intelligence were involved, how do I get to a godly intelligence? Concerning just the NT, which is the basis of Christianity, the NT writers actually give this away where all of them rely on other sources to basically reverse engineer the character of Jesus based in particular on what the Septuagint (Greek translated OT) said. How the writers wrote is like telling a story where they tell you things about Jesus when he is supposedly alone. Luke comes right out at the beginning to tell you he is not an eyewitness, nor does he know any. Mark also tells you he is telling the tale told to him by Peter if I remember right. Matthew claims to be getting some information from Paul and you can see where he borrows "incorrectly" from the OT as you can with the other writers. For example, Isaiah 7:14 talks about a child named Immanuel that is meant as a "sign" for his King Ahaz where in Isaiah 8 he informs us that "all" of his children are "signs" for his country. Matthew borrows this to wrongly claim that Isaiah was forecasting the future Jesus some 700 years later, even claiming Jesus is known as Immanuel, demonstrating he is borrowing from Isaiah. There are many, many of these kinds of examples demonstrating a reversed engineered Messiah. Even the suffering servant in Isaiah 53 (actually begins at end of 52) is clearly identified as the nation of Israel, with Isaiah himself literally calling the servant "Israel" several times leading up to this passage and even tells us the "suffering" already took place in the past because he was talking about the suffering of Israel at the hands of the Babylonians and why that suffering was necessary. Finally there is the history of Christianity that was not a huge movement but rather a slow, multi-group movement that followed different books concerning the story. It was only when Emperor Constantine used Christianity for political reasons that it stuck like it did. Like I said, I could write a book but another great source to look at are the stories of ex-christians who figured out it was man made for completely different and various reasons, but most make very reasonable cases for their departure and compare the biased delusions as a christian and often wanted to become a better christian and decided to learn more only to discover they have been duped. This sort of leads to looking into ex-preachers/pastors and atheists who once believed until they got their degree in theology to learn the ugly truth about Christianity but were torn with what to do after spending all that time and money to become a pastor/preacher only to do their best for spiritual guidance, while not actually believing in the religion.