Good point, I think. It appears from all accounts that Twain was very
cynical about the United States in the mid-1870s, long before the string of
calamities that plagued his family life and his business ventures.
I like the idea of his being "hurt and disappointed" by evidence of human
shortcomings, too. It's always seemed to me that Twain clearly enjoyed
people -- not necessarily loved them, but just enjoyed them, was amused by
them. And some of his most bitter diatribes result when their actions don't
live up to his expectations and put an end (for a while) to his enjoyment of
their lesser foibles.