I.e., the doctor is not a callous man, it's just that he can't tolerate anybody!

This summation of Monygham's nature shows clearly that his cynicism is based on a fundamental compassion. But it also sets out a grim dichotomy in which "tolerance" can only be achieved by lacking that compassion -- by being callous. "Tolerance," of course, is what is necessary for people to live together in society, to be men "of the world"; in other words, a successful society is a callous one. Monygham rejects this tolerance in favor of "passion" and "sensitiveness," which, we recall, were attributes of Costaguana's most unsuccessful periods -- see Decoud's exasperation that "We have political passions" , and the "great sensitiveness" of a certain sadistic officer.