Answer: to compare loneliness to an undesirable illness or disease that is difficult to cure.
Carson McCullers uses the term "malady" to refer to loneliness in America in order to draw a parallel between this social condition and an undesirable illness. Loneliness has become a serious problem in the country, and it will continue to do so as the population ages (older people tend to suffer more from loneliness, but they are not the only ones). Just like a disease, loneliness can be very difficult to diagnose and to cure. Moreover, it can negatively impact the quality of life of those who suffer from it.
