The story clearly develops from the flaws in Baba's and Amir's characters. Any master will enjoy a superior economic and social position over a servant, but Baba's and Amir's actions were not determined by their positions in the household. Baba betrayed Ali out of lust for Ali's wife, and he betrayed Hassan, his own son, out of guilt, shame, and fear for his reputation. Baba treated Hassan well, but he betrayed him by refusing to acknowledge him as a son.
Amir often treated Hassan cruelly, not because he was a social superior, but because he felt jealous of him. Baba treated Hassan with warmth and acceptance, which Amir deeply resented since his own relationship with Baba was so lacking. Amir betrayed Hassan's friendship with his cruelty, and eventually he betrayed Hassan by running away in fear rather than take any action to protect him from the bullies. Finally, Amir betrayed Hassan by scheming to have him sent away from the household. This he did out of guilt. Amir could not stand to live with Hassan any longer. The boy's mere presence reminded him of his own cowardice.
Baba and Amir betrayed others not because they were masters to servants, but because they were flawed human beings.
When you pose the question in the way you do, as an either/or approach, you may miss some of the nuances. Why does it have to be either/or? What can't there be elements of both? In life, which is complex, the answer is almost always found in between. In fact, answers are messy and at times completely inconsistent. So, I would say that there are elements of master/servant dysfunctions as well as character issues. For example, if there is a strong cultural differences between master/servant, then it would be hard to see outside of this. Also in a culture based on shame, there is almost unbearable pressure to act a certain way. If you know this, then you can see the character is not the only dysfunction. Society has a role as well.
In the book "The Kite Runner" the reader learns about the relationship between the classes of people called the Hazara's. Baba was raised in a time when they were considered to be a lesser people in his community. He was aware of this throughout his life. The book talks about him growing up with the child Ali as his brother and fried, but Baba does not recognize him as a friend. Ali is the same way even though he spends twelve years playing with Hassan and experiencing life with him in the same manner that Baba had with Ali. Because of this type of innate mentality ingrained in them by the social order of the society, I can not define their behavior as a character flaw, especially in Amir. In the end Amir takes his step brother's son into his home and defends him for his identity as a Hazara. He has risked his own life for a Hazara when he could have walked away. Baba had spent his lfie trying to make up for what he identified as his sin, his relationship with Ali's wife.
I believe that the privileges taken and the behavior exhibited stemmed from their social class and the class of Ali and Hassan, servant versus master relationship.
"But in none of his stroies did Baba ever refer to Ali as his friend."(25)
"The curious thing was, that I never thought of Hassan and me as friends either."(25)