Similar to embarrassing details, some aspects of the New Testament would not have been included if they had been a fabrication.
Take for example Joseph of Arimethea:
Joseph is credited in all four Gospels as burying Jesus in his family crypt after His death. But, Joseph was a member of the Sanhedrin, the very party responsible for crucifying Jesus!
If this was all a lie, there would be no reason to portray a member of the guilty party in a positive light.