why dose his father get angry?

During breakfast one morning, Reuven mentions that some are saying that it is time for Palestine to become a Jewish homeland and not only a place where pious Jews go to die, not mentioning that this is his father's idea. Reb Saunders becomes enraged, and says that the land of Abraham, Isaac and Jacob will not be built by Jewish goyim while he lives. Later, Reuven says that he did not know that Zionism is a contaminated idea, and Danny asks not to mention a secular Jewish state again, for it touches a nerve. Danny admits that his father is suffering for the six million Jews who have died, and Reuven worries that Reb is sick.