I find Wikipedia a useful jumping off point in general to get a sense of common criticisms on a variety of topics. In this case, I'd start in the Reception section of Sowell's:
Are you referring to Economics in One Lesson? It looks like that's Henry Hazlitt, not Sowell. (Am I missing something?) It looks like DeLong has some criticism of that.
Just to be clear, I'm not an expert on any of this. I just popped in to provide a pointer I've found useful in learning about a topic when I'm not sure where to start. Similarly here, I just applied a bit of search-fu.