As a benchmark for this topic one could do worse then :

Vitamin C, Linus Pauling Institute"

http://lpi.oregonstate.edu/infocenter/vitamins/vitaminC/index.html

They discuss what is known about vit c as regard to disease treatment and
how much might be needed; from a scientific point of view.  Having not
read the Levy book it is hard to speak of it's scientific merit.  Having
1200 refs is not the same as being scientific valid as he sees the
question.  Looking at a few of his blurbs on the net is intresting.  In
reference to the 1200 refs he says he saw a pattern in the clinical
information, which means in the usual sense the reports of doctors when
using it and their reports of apparent changes.  While suggestive and
makes it worthy of doing science about this intresting question, it is not
scientific confirmation.  Another of his blurbs is an example.  He had two
west nile virus folk take lots of vit c and they got better as gauged by
the level of symptoms change.  This is intresting but is not "proof" as is
required in science.  A research using hiv for example would be something
like this.  Two groups of hiv people are matched by age, weight, stage of
symptoms etc. into those who use current approaches and one using same but
with the addition of vit c.  Not only would a change in symptoms be an
supporting outcome, but the level and even possible absense of the hiv
virus would be strong support in the question.  This is the difference
between the "trial and error" and see what happens to symptoms type of
medicine and the evidence based controlled research driven medicine
illustrated above.

As to commercial conspiracy to keep this from being known or practiced, it
all depends on whose commercial intrest ox is being gorged.  ATM is
perhaps the world's largest graim company and producer of grain derived
products.  When they produce high fructose corn sweetner they also produce
vit e and vit c as by products.  They would be happy to provide all the
vit c you might want, as corn is the most common source of it and the have
a very very big chunck of the corn market and vit c markets.  Does this
mean this company, and similar, are the real driving source of dr. levy
and this kind of book?  Levy is in the state of co., right next to the
grain growing area of the country and ADM is a very large contributer to
politicians and research at universities.  The pattern is emerging and the
conspracy affot watson.  Where is the nutrition theology when we need it
most?