My thesis can be stated simply: scribes occasionally altered the words of their sacred texts to make them more patently orthodox and to prevent their… - Bart D. Ehrman

Christianity may well have succeeded even if Constantine had not converted.

One of the most amazing and perplexing features of mainstream Christianity is that seminarians who learn the historical-critical method in their Bible classes appear to forget all about it when it comes time for them to be pastors. They are taught critical approaches to Scripture, they learn about the discrepancies and contradictions, they discover all sorts of historical errors and mistakes, they come to realize that it is difficult to know whether Moses existed or what Jesus actually said and did, they find that there are other books that were at one time considered canonical but that ultimately did not become part of Scripture (for example, other Gospels and Apocalypses), they come to recognize that a good number of the books of the Bible are pseudonymous (for example, written in the name of an apostle by someone else), that in fact we don't have the original copies of any of the biblical books but only copies made centuries later, all of which have been altered. They learn all this, and yet when they enter church ministry they appear to put it back on the shelf.

A storyteller who made up an account about Jesus in order to prove a point may well have known that he was passing off a fiction as a historical event. A scribe who wanted a text to say something other than what it did may well have changed the text for just that reason. In some cases it is hard to imagine how else the resultant deception could have come about. Whoever added the final twelve verses of Mark did not do so by a mere slip of the pen.