The Mahabharata is the most wonderful book in the world; there can be no doubt of its authenticity because it depicts people not as heroes or saints but as they are. The Rishi’s faults are pointed out and the good points of even evil persons are mentioned. It is a retelling of what happened as it did happen. Which is why it is called an Itihasa.
There is no one who is entirely bad, no one who has always been entirely good. In a human being is the whole universe, good bad and middling; clever mediocre and foolish. In him resides all the beings, including devas, asuras Rakshasas and pisachas. In him are munis like Durvasas and noble beings like Uddalaka Aruni.
As an American poet wrote,
Do I contradict myself?
Very well, I contradict myself
I am large, I contain multitudes
This is seen in the Mahabharata where nobody is a totally evil person or a totally good person. Even Duryodhana is not blindly judged. And this is one powerful reason to believe that the Mahabharata is an historical text and not a mythological fancy of an inspired Rishi.