When Bart Ehrman previously appeared on The Colbert Report, it was to promote his book Misquoting Jesus: The Story Behind Who Changed the Bible and Why (HarperSanFrancisco, 2005). That time, he gave the impression that we can't trust the New Testament because we don't have the original manuscripts and the copies are not all exactly the same. What Ehrman knows to be true does not always match what he wants to tell the world, both because he wants to promote agnosticism (and destroy Christianity) and because sensationalism sells books.
http://watch.thecomedynetwork.ca/the-colbert-report/interviews-a-z/interviews-e/#clip16311 But I've read Misquoting Jesus and I found it rather non-threatening. Here are some highlights:
“And so we must rest content knowing that getting back to the earliest attainable version is the best we can do, whether or not we have reached back to the ‘original’ text. This oldest form of the text is no doubt closely (very closely) related to what the author originally wrote, and so it is the basis for our interpretation of his teaching.” (p. 62)
“Modern scholars have come to recognize that the scribes in Alexandria-which was a major intellectual center in the ancient world-were particularly scrupulous, even in these early centuries, and that there, in Alexandria, a very pure form of the text of the early Christian writings was preserved, decade after decade, by dedicated and relatively skilled Christian scribes.” (p. 72)
“It is probably safe to say that the copying of early Christian texts was by and large a ‘conservative’ process. The scribes-whether non-professional scribes in the early centuries or professional scribes of the Middle Ages-were intent on ‘conserving’ the textual tradition they were passing on. Their ultimate concern was not to modify the tradition, but to preserve it for themselves and for those who would follow them. Most scribes, no doubt, tried to do a faithful job in making sure that the text they reproduced was the same text they inherited.” (p. 177)