The criteria for what makes a tragedy have shifted quite a bit over time. In ancient Greece, Aristotle wrote that in order to have the desired cathartic impact on the audience, a tragic figure should be a king or other elite figure afflicted by a wrathful or vengeful god. Shakespearean tragedies still feature nobles, but the basis of the tragedy is human conflict (between individuals, as well as psychologically within a single individual), not divine. Many modern tragic figures (e.g., Willy Loman in Death of a Salesman) are ordinary people, beaten down by everyday problems. The Walter White story arc is interesting because he starts at the bottom and works his way up, becoming tragic by virtue of his "success." As many have noted, tragic figures like Heisenberg and Rorshach seem to attract a lot of misplaced enthusiasm, but this isn't a new phenomenon - Hamlet, Faust and the Lucifer of Paradise Lost have always had many admirers despite their tragic nature. Maybe the next phase in tragic nareative structure will entail stories that are intended by their authors to serve as a warning, but which tragically get reinterpreted by audiences as celebrating the character flaws they were written to caution about.