essay question: what idea does the author develop regarding the impact and cause of alienation that individuals may experience?

I guess you could also make a case for other marginalized characters as well. Cetrainly Tom Robinson, as are many black characters, has his share of alienation and persecution. The cause is certainly racism and ignorance (they go hand in hand). The result is that, despite a most excellent lawyer in Atticus, he is powerless against the hate of the larger white community. Even Bob Ewell is alienated, largely by his own doing. His life is the most pathetic for he not only becomes a social pariah he also punishes his daughter Mayella in the worst way possible.