To give a darn means to care about someone or something, but in this sentence the people who cared a great deal before suddenly become believers.
Consider the statement "So when it's the end of the world, kincaid was saying, people who cared a great deal before suddenly become believers.". Is the statement "So when it's the end of the world,kincaid was saying, people who didn't give a darn before suddenly become believers." false? Yes/no/unknown