(Note: I apologize for bringing Glenn Beck back into our collective imagination)
After reading Economics in One Lesson, my first impression was that it read like a rhetorical playbook. Indeed, it could aptly be renamed "Arguing with Idiots: How to Stop Small Minds and Big Government." Hazlitt of course would dismiss Beck as too "emotional" and not "logical" enough, but both do seem to target the same group: liberal "Statists" who have no common sense. Liberals, in this respect, are painted as either short-sighted, idiotic, or too emotional as to be irrational--after all, how can they fail to understand something so "elementary" and common-sensical?
Hazlitt's purpose is to provide his audience with the necessary rhetorical tools to point out the so called "fallacies" and "logical contradictions" of New Dealers, labor supporters, and other "Statists." It gives you a vocabulary, which if used, sets up the debate on terms favorable to the defenders of the "free market." Taxes become a kind of "theft"; good intentions of liberals become naive and short-sighted; and government becomes an institution filled with bungling bureaucrats and" parasites."
Most importantly, Hazlitt constructs the economic debate around logos--specifically, formal validity. According to Hazlitt, economics is an objective "science" much like "mathematics." Like science, economics too has its own nomologically fixed laws. Thus, we can start with certain premises and deduce logically necessary "implications." Of course, much of what Hazlitt writes is true and taught in many "Introduction to Economics" courses. But perhaps, his main fault is that he leaves out the disclaimer: ceteris paribus. He mistakes simple economic models as reality itself.
However, from a rhetorical perspective, I think his biggest fault is that he short-sightedly concentrates on logos at the expense of ethos and pathos. He therefore fears concepts such as "justice" and "fairness" because they are "nebulous" and can't be defined in necessary and sufficient terms. Nonetheless, it does seem contradictory that, on the other hand, he believes that terms like "freedom" or "essential government functions" are not nebulous and can be rigorously defined.
Therefore, while his arguments may be formally valid, he ignores the fact that notions of freedom, essential government services, justice, fairness, etc. are concepts open to rhetorical contestation. To ignore this feature about these ideas is to deny a politics of democratic discourse.