If Jesus is divine then why does his family say he was out of his mind in Mark 3:21?

Going with the idea, for the moment, that Jesus was a real person, Mark's Gospel presents us with evidence in the text that there was no "immaculate conception." In Mark, there is no conception and birth story. Joseph the father of Jesus (written of in Matthew and Luke) is not even mentioned, and Jesus is referred to as "son of Mary" (see Mark 6:3). This is something that was not done in Jewish society - a man was not referred to as the son of his mother, as the paternal line was what gave a man an esteemed identity. He had no honor in his hometown, and people who knew him widely believed he was an illegitimate child. In light of all of the above, it is not surprising that they thought him insane. The other Gospel writers present different stories with different implications.