There is a certain amount of subjectivity to the two questions being asked here. I think that most definitely the story is making a statement that humanity and human decency can be found in all kinds of people. I believe that the story is making a strong case that a hope in humanity can be found even among people that civilized society deems as outcasts.
John Oakhurst, Mother Shipton, Uncle Billy, and Duchess have all been kicked out of town for being morally corrupt or morally suspect, and Uncle Billy proves that he most certainly deserved the town's wrath when he steals from the group in order to save himself; however, the other members of the group prove to be incredibly kind, loving, and selfless. John Oakhurst, for example, stays with the group the entire time, despite knowing that he has a much better chance for survival on his own. Mother Shipton selflessly sacrifices herself and starves herself to death so that Piney has a better chance at survival. The group as a whole protects Tom and Piney from Uncle Billy's aggression and rude comments. There is irony in the fact that the outcasts show far more compassion to their fellow humans than the people from Poker Flat, who are supposed to be the moral and honorable people.