Another major argument against suggesting that the gospel writers doctored their accounts is that this process would have had to occur during the lifetimes of the apostles.
If the apostles had connived in the process they would have been responsible for deliberately and knowingly altering the teachings of their own master. Yet these were men prepared to lay down their lives for their testimony. Some at least would inevitably have spoken out strongly against any such attempt. And even if they had not done so, the enemies of Christianity would have been quick to point out how the original story had changed. Yet no record exists of such a dispute in the first century.
Those who advocate this view would have us believe that, somehow, all such records were ruthlessly and successfully suppressed. Yet Christianity was widespread by the beginning of the second half of the first century, making such suppression impracticable.
The NT documents do in fact make reference to some areas of doctrinal disagreement in later years. The issue of whether or not Christians should follow the Old Testament regulations was a major issue, for example, and there are many references to it. But the only mention of dispute with regard to the gospels or the essential facts of Jesus' life and teaching during this period concern a few individuals, far removed from the events themselves. For example, 1 John 4:2-3 and 2 John 1:7 mention deceivers who denied that Jesus had come in the flesh: but it is clear that this represented a denial of accepted Christian belief and is almost certainly an allusion to the Gnostic heresy that appeared in Greek, rather than Jewish, circles towards the end of the first century.
Likewise, there are plenty of records of doctrinal disputes, heresies, etc., in surviving church records from the second century onwards. So, for any significant alteration of Christian doctrine to have occurred without leaving any trace of the controversy that would inevitably have resulted is just not credible.