Why does Twain seem to always portray teh con men's victims as either greedy or foolish themselves?

Although the duke and the dauphin become increasingly malicious and cruel in their scams, Twain continues to portray the victims of the con men’s schemes as unflatteringly as the con men themselves. The duke and the dauphin’s production of The Royal Nonesuch, for example, is a complete farce, a brief, insubstantial show for which the audience is grossly overcharged. But what makes the con men’s show a real success, however, is not any ingenuity on their part—they are as inept as ever—but rather the audience’s own selfishness and vindictiveness. I think that Twain is touching on the dark side of general human nature as opposed to Huck's relatively enlightened moral code.