The correct answer is option 3: to compare loneliness to an undesirable illness or disease that is difficult to cure.
Explanation:
Carson McCullers uses the term "malady" to describe loneliness as a disease that is difficult to cure because by using this term he tries to show how many American people suffer from being alone. They can't stand feeling lonely or having to be on their own. Isolation is the main curse for the American people. They always need someone around to make them feel good about themselves or reassure who they think they are.
It helps you clearly express your argument. You are trying to convince the auidence that your point is valid. So when thinking about the auidence, you decide the tone of your writing and how simple and complex it should be.