I've read some of the stuff written by people who question the historical existence of Jesus.
The denial is called "The Jesus Myth" and was started by a 19th century historian, Bruno Bauer who had an influence on the atheism of Karl Marx. It wasn't until the early 20th century that some started published books about it. There have been Mytholigist/authors since then who were untrained in historical studies but tried their hand at "The Jesus Myth". Today, the question of Jesus' historicity is effectively dead in the scholarly community.
Most authors who attempt to deny that Jesus existed start by throwing out all Christian writings, saying they are biased or simply fictional works. Some authors attempt to state that Christian writings (especially the Gospels) were not written until the 2nd century between the years of 100 AD to 199 AD. They then go on to discount non-Christian writings (like those of historian, Josephus) and attempt to establish the old "Nazareth did not exist" argument. Such arguments easily dispatched. Their efforts are easily seen as attempts to discredit evidence against their pet theory by saying all the evidence they don't want to see was written by liars.
All such arguments are based on a logical fallacy called
Ad Hominem. Arguments of this kind focus not on the evidence for a view but on the character of the person advancing it; they seek to discredit positions by discrediting those who hold them.
Historians counter these arguments by showing evidence of the controversy that occurred between those in Jerusalem and the Christians who taught that salvation was being extended to Gentiles (non-Jews). Clearly, had they had the even slightest reason to think that Jesus was a fiction who never existed, they would not have expended so much energy arguing that he was not the Christ, the Messiah promised of God to the seed of Abraham.
It's interesting that the Mythologists don't try to deny the existence of writings of Paul. Instead they attempt to bend his writings to their own purpose.
Others have tried to say that Jesus did exist but that he didn't "come to earth" in human form. Docetism is an opinion held primarily by early Gnostics that Jesus had no human body and only appeared to have died on the cross. They manufactured a heresy that affirmed the historical reality of Jesus but denied his true humanity. Obviously, this is no Jesus Myth since it affirms the historical Jesus. But these innovative approaches to the issue create a problem. If Docetists were looking for a way out of the paradox (explaining how a man of flesh could show the nature of God), why not return to the supposed Mythical Christ view?
The writings of Paul presume a Jesus who lived, acted, and taught; whose life was a model for believers, and who died on the cross. Paul did not waste any effort in attempting to prove that Jesus existed because there was no controversy there. His unique aim was to prove (what the Jews refused to admit) that Jesus was the Christ. Other writings focused on refuting the "God-Man" theories of the Gnostics.
1 John 2:22-24
Who is the liar? It is the man who denies that Jesus is the Christ. Such a man is the antichrist—he denies the Father and the Son. No one who denies the Son has the Father; whoever acknowledges the Son has the Father also. See that what you have heard from the beginning remains in you.
1 John 4:1-3
Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.
It is interesting to me that even today (in our supposed modern world) many continue to adhere to the 19th Century idea that the man did not exist. The very fact that there is so much effort expended on this subject, and zero effort expended denying the existence of other historical figures is significant.
OT: If Jesus had married his closest friends were unaware of it.
