I disagree with Bryan Caplan's argument that mental illness is a false category; he is making an odd turn toward behaviorism. That the behavior can be reduced to preferences and constraints does not mean that is the best or only way of understanding the phenomenon (which is not just about behavior).
He misstates my position. My claim is not that mental illness is a false category, but that "weird behavior stems from illness" rarely fits the facts as well as "weird behavior stems from weird preferences." And if anyone's being behaviorist, it's orthodox believers in mental illness, who just can't imagine that people do weird things because they genuinely want to do weird things.
I do agree, though, that there are "other ways of understanding the phenomenon" [of mental illness]. But the "other ways" that have insight to offer are ethics and philosophy, not medicine and neurology. Consider: If people didn't think that alcoholism was bad, would anyone bother to argue that it was an "illness" or stemmed from a "chemical imbalance"?
P.S. The irony of Tyler's hostility to the Szaszian critique of mental illness is that his Create Your Own Economy (now The Age of the Infovore) is essentially a Szaszian interpretation of autism. If only he had built on this foundation - or even acknowledged the parallels - I think the book would have been much more compelling.