Note: Wallace has written a summary of the debate. Ehrman's argument is that "even though we have thousands of manuscripts of the New Testament, we do not have many *early* ones — and hardly any *really* early ones. That is why we can not (always? ever?) know with absolute certainty what the authors of the New Testament originally said. That matters for lots of reasons, one of which is that fundamentalist Christians but their faith in the very words of the Bible. But what if, in some passages, we don’t know what those words were?"
Comment: The history of early Christianity is about as murky a subject as you'll ever find. The origins of the New Testament and the dating of early NT manuscripts is even more obscure and contentious, and I guarantee that if you start researching this with an open mind, you'll never come to any definite conclusions. The whole field has been muddied by guesswork, confirmation bias and a lack of hard physical and documentary evidence. As of now, the only thing we know for sure is that Christianity emerged in the Roman empire during the 1st - 4th centuries AD. How this happened is unknown unless you take the NT literally and accept the history of the Roman Catholic church.