What is the evidence in chapter 24 that racism is a disease that infects a person's mind and soul?

In chapter 24, Aunt Alexandra has ladies over for a meeting of the Missionary Society of Maycomb. The ladies feel compassion for the Mruna people: they are Africans who live in poverty but have been converted to Christianity by a missionary named J. Grimes Everett. At the same time, the women use offensive language about blacks in their own community. They fail to see the obvious irony in their statement. They are so infected with racism that they do not even understand their hypocrisy.