What did Baba do wrong in The Kite Runner?

In The Kite Runner, Baba is certainly an imperfect character, but mostly because of his upbringing in a society in which his ethnicity, religion, and wealth place him in the ruling class. Within the limitations of that upbringing, he is by no means an evil man.  The most striking wrongdoing on Baba's part is his coupling with Ali's wife, Sanaubar, which results in the birth of Hassan.  This wrongdoing on his part, kept secret...

In The Kite Runner, Baba is certainly an imperfect character, but mostly because of his upbringing in a society in which his ethnicity, religion, and wealth place him in the ruling class. Within the limitations of that upbringing, he is by no means an evil man.  The most striking wrongdoing on Baba's part is his coupling with Ali's wife, Sanaubar, which results in the birth of Hassan.  This wrongdoing on his part, kept secret through throughout the novel, leads to his guilt, his loving treatment of Hassan, albeit as a servant, and his not so loving treatment of Amir, who is a less pleasing child.  This wrongdoing leads to Amir's resentments also. Although Amir has no clue as to the source of his resentments, he feels the undertones of the relationship between Baba and Hassan, a love that he cannot seem to gain for himself. All of these undercurrents drive the action of the novel and the feelings of its characters.  This is a toxic secret, but of course, in that time and place, disclosing it would have been even more toxic, possibly leading to death. I think it is fair to say that Baba was immeasurably regretful about his wrongdoing and did the very best he could thereafter.