In The White Tiger, is Balram justified in killing Ashok?
Certainly, murder is never justified. As the other educator pointed out, Balram did not kill as an act of self-defense, nor did he kill Ashok to protect anyone. For his part, Balram was solely motivated by his desire for revenge.
Having said this, Ashok was no angel. In fact, his behavior was often repulsive and his actions abhorrent. It was Ashok who let Balram take the blame for Pinky Madam's actions. In the story, Pinky Madam ran over a child while driving intoxicated. Instead of stopping to see to the plight of the child, Ashok conspired with Balram to leave the scene of the accident. When Pinky Madam protested, Ashok gagged his wife to keep her quiet.
At their home, Ashok dragged Pinky Madam upstairs, with a scarf still tied to her mouth. Later, Ashok made Balram sign a statement identifying him as the sole party responsible for killing the child. Despite his seething anger, Balram had to keep his emotions under check. He maintained that the jails of Delhi were full of drivers behind bars because they were "taking the blame for their good, solid middle-class masters." A poor man could leave the villages, but the masters of the Coop still owned them "body, soul, and arse."
Balram was further incensed by the fact that his own grandmother supported the prospect of his incarceration. In India, it is a matter of pride for impoverished families to support the sacrifices their sons and daughters make for their masters. Even the judges take bribes for choosing to ignore the real facts about each case. The one left holding the bag, of course, is the driver himself. This state of affairs is what leads Balram to contemplate killing Ashok (and to finally go through with it).
Since men like Balram have no recourse to justice, they resort to administering their own brand of equity. Balram's actions (and also Ashok's) demonstrate the impact of corruption on both the rich and poor.
No, in my opinion Balram is not justified in killing Ashok. There is no doubt that Ashok is a "bad guy." He's an abusive drunk through much of the story. He's an incredibly selfish individual as well. He's wealthy enough to have two private drivers, but when Ashok takes Balram to Dehli, Balram is forced to live in a cockroach infested apartment, while Ashok and his wife live in splendor.
At one point in the story, Ashok beats Balram for taking his wife to the airport without his knowledge. Ashok also likely has ties to organized crime which is indicated by the bag of money he's always carrying around to use to bribe public officials. Ashok is a selfish and corrupt businessman more or less.
I might feel differently about Balram's justification of killing Ashok, if Balram had done it out of self defense or had done it to protect someone else. I just don't get that feeling. Balram lured Ashok from the car and killed him with a bottle. Ashok then took the money and used it to set up his own business AND begin bribing officials to ensure the success of his new business. I don't see Balram being much different from Ashok. It's simply a substitution of one corrupt businessman for another.