I have bought the book, but I have not gotten around to reading it
except I did read the appendix about "The Mad Genius Problem". In
the discussion about "madness and genius", Szasz spends a couple of
a paragraphs discussing the ideas and work of Francis Galton, the
famous cousin of Charles Darwin.

Szasz argues that the idea of a "mad genius" is rather nonsensical.
He says the idea of "genius" is too vague to say that somebody is a
genius and, of course, Szasz does not believe in "madness". So
Szasz thinks talking about "mad geniuses" serves no real purpose. I
don't argue with that.

Szasz goes into a brief discussion about the ideas of Galton, and
Szasz sets out to belittle Galton's ideas by comparing Galton's
remarks about the heredity of "genius" to the ideas of "the modern
psychiatrist" who "knows that "manic depression is hereditary".
Therefore, Galton's ideas are no better than the ideas of "the
modern psychiatrist". I would point out that "manic depression" may
very well be hereditary. Just because "the modern psyschiatrist" may
say that md is hereditary does not mean it is not hereditary, if
that is what Szasz is implying. Of course, I would agree with Szasz
that md is not an illness as defined by Virchow. However, if md is
a personality trait maybe it is a trait or behavioral tendency that
is inherited.

For some reason Szasz seems to be very suspicious of "genetics".
Galton's research on "genius" really led to the research
on "intelligence". And actually Modern research has shown
that "intelligence" is a characteristic or trait that is primarily
produced by heredity or genetics. People do not become intelligent
because of the environments they grow up in. They are intelligent
because of DNA that is transmitted to them by their parents. But
for reason that idea seems to bother Szasz, as one can see from his
remarks about Galton. Szasz says, "Edison knew neither genetics nor
psychology, but he knew what genius was firsthand. It was, he
said, 'one per cent inspiration and ninety-nine per cent
perspiration'." Whose perspiration and inspiration was Edison
talking about? Just any old Tom, Dick, or Harriet? Edison did not
just hire anyone to work in his laboratories.

The word genius is usually assumed by most people to refer to
someone who has an extremely high IQ. However, I remember from my
days as a psychology student that psychologists preferred to not use
the term genius in that context. A genius was a person who had made
some remarkable discovery in science. A genius may have a high IQ
but having a high IQ does not make a person a genius. Making a
significant discovery is the criterion associated with genius.
Working out some abstract chain of reasoning that no one had done
before.

A mad person may profess some bizarre idea or make some bizarre
claim that he cannot prove. And a "genius" may profess what is
ostensibly a bizarre idea. However, the mad person's idea is
probably not an accurate depiction of "reality", it is probably some
value judgment that is not grounded in reality. The genius, on the
other hand, probably has discovered some "facts" or has connected
some facts that do reflect reality, which nobody prior to that time
had noticed. The genius can prove his claim. Nobody may understand
or take the time to consider the proof at first, but eventually the
proof is understood and replicated.

Will stop here and wait for comments.