Most skeptics assume the New Testament is biased. Therefore, they demand sources that are written about Jesus outside the New Testament. Furthermore, these sources need to be written by non-Christians, which equates to pure objectivity and no propaganda.
Sadly, the demand for this wish list shows the ignorance about the oral world of Jesus. We have a section on oral tradition here.
Maurice Casey, a non Christian scholar who specialized in early Christianity summarizes the importance of the oral world of Jesus:
“The major reasons why all our earliest sources for the Life and Teaching of Jesus are Christian is that Jesus was a first- century Jewish prophet who lived in a primarily oral Jewish culture, not a significant politician in the Graeco-Roman world. By contrast, for example, Julius Caesar was an important political and literary figure in the highly literate culture of the Romans. It is therefore natural that he should have written literary works which have survived, and that other surviving literary sources have written about him.”
Casey goes onto say:
“Jesus of Nazareth left no literary works at all, and he had no reason to write any. He lived in a primarily oral culture, except for the sanctity and central importance of its sacred texts, which approximate to our Hebrew Bible. A variety of works now thought of as Apocrypha (e.g. Sirach) or Pseudopigrapha (e.g. 1 Enoch) were held equally sacred by some Jewish people, and could equally well learnt and repeated by people who did not possess the then- difficult skill of writing. Almost all our surviving primary sources about Jesus are Christian because most people who had any interest in writing about him were his followers,and the few relatively early comments by other writers such as Josephus and Tacitus are largely due to special circumstances, such as Jesus’ brother Jacob (Jos.Ant .XX,200), or the great fire of Rome” (Tac.Annals XI, 44). – Jesus: Evidence and Argument or Mythicist Myths? by Maurice Casey