I'm a little concerned that this blog is focusing too much on creationism and evolution, so I'm changing things up a bit. When I purchased Why Evolution is True, I also picked up Jesus, Interrupted: Revealing the Hidden Contradictions in the Bible (and Why We Don't Know About Them) by Bart Ehrman (which I'll refer to as "JI"). I'm now reading both of these and will alternate writing about each of them here.
Early on, Ehrman presents two basic facts that go a long way toward explaining the "why we don't know about them" portion of the book's title. On pages 3–6, he says that modern Mainline Protestant seminaries include classes that use the historical-critical method, which focuses on the historical context of the Bible and the original intentions of its authors. From these classes they learn a significant amount of information about the various problems with the Bible: historical errors, authorship issues, contradictions, and the like. This was a pleasant surprise to me, since I had assumed that such an approach was taken primarily in secular universities.
However, on pages 12–14 Ehrman describes an interesting phenomenon: none of the pastors who learned this information – not even those who accept it – get around to actually sharing it with their congregants. Despite the knowledge they've gained, they simply preach from the "devotional" approach (e.g. how does passage X apply to your life) and ignore the historical-critical method. They generally don't even mention the critical approach in order to dismiss it – they just pretend it doesn't exist. I can personally attest to this; the pastors I've listened to seldom (if ever) mention any serious criticism of the Bible.
One possible explanation that Ehrman gives for this is very telling: he wonders if pastors are "afraid that historical information might destroy the faith of [the] congregation". This possibility is worrying to me. If pastors intentionally omit critical information to preserve the faith of their flock, it's only a small step from there for them to (for example) exaggerate or even fabricate miracle stories to add to that faith. They could easily rationalize this by saying that a few white lies are a small price to pay for keeping people out of an eternity in hell – and if Christianity was true, I'd be tempted to agree.
On pages 20–22 Ehrman gives a second reason for the general lack of knowledge about Bible errors. Most people either read the Bible in patches (e.g. a few verses from James here, a chapter from Acts there) – or sequentially (e.g. Matthew from start to finish, then perhaps continuing with Mark). This latter method Ehrman calls the "vertical" approach. He contrasts this with the method that critical scholars use: the horizontal approach. With this method, multiple books of the Bible are compared side by side. By examining them in parallel, scholars can easily pinpoint errors and contradictions, as well as major differences in authors' approaches to essential Christian doctrines.
Essentially, there are two main ways Christians could potentially learn about the problems with the Bible: by going to church or by reading it on their own. But their pastors won't tell them about the problems, and their reading method isn't the best one for finding those problems. And of course, the small fraction of people who find out anyway usually want to continue believing, so they can always use the resources of apologetics to rationalize and explain away any issues they encounter. This combination of poor access to information and confirmation bias allows Christianity to thrive despite the clear problems with its holy book.