There are some millionaires With money they can't use (14-15)
Why does Angelou single out millionaires? It's probably to emphasize that loneliness crosses all social and class barriers.
They've got expensive doctors To cure their hearts of stone. (18-19)
Once again, healthcare fails us! Money can only buy certain forms of healing – and the alone-ness that this poem describes doesn't seem to respond to traditional healing methods.
The race of man is suffering (30)
By assuring us that all of mankind belongs to a single "race," Angelou erases all social or cultural barriers. Everyone is suffering, regardless of his or her circumstances.