There are several things which keep going around in circles in relation
to foods, and the reason they do go around in circles and why no real
headway can be made is because there simply is not enough data.
Nutritional research in humans is recent enough that new info has people
recanting all over the place repeatedly, for example 1, at one point
fruits were thought to be little more than sugar packets but now we know
that many, especially the very pigmented ones, tend to have a wide range
of compounds which help as antioxidants and more, for example 2 we are
just now learning some of the ways that the human body deals differently
with whole grains as opposed to highly processed ones, and the list goes
on and on.  Now for ferrets we are talking about an animal which doesn't
have a lot of decades of the types of research behind it that serve the
desires of their families, plus that is on top of so much of nutritional
work in general being so new.
 
So, once a person is providing a diet which eliminates or greatly reduces
the KNOWN dietary problems (See _Biology and Diseases of the Ferret_ for
the best sections on these.) then pretty well most food viewpoints on
ferret diet become debatable.  There are highly reputable vets who favor
one or another viewpoint, ditto highly reputable ferret owners.  In such
instances no matter what the person chooses, as long as he or she knows
the known or postulated risk factors, NEITHER IS CURRENTLY WRONG.  They
just are personal choices at this point.
 
Eventually, perhaps one or another choice will be known to be better, but
this isn't a popularity contest, it is a set of questions which need to
be answered to even get to the point where the true answer of which diet
is healthier simply must be answered.
 
I know that there are those who explain the viewpoint, which boils down
to "What is most akin to the wild diet is probably most healthy." and
there are a LOT of good reasons to follow that philosophy.  It is the
diet which the animals' ancestors adapted toward which as a result
maximizes their population's reproductive success in the environment
available.  One place that this approach falls apart is that the
environment available has changed, particularly in terms of medical care.
Even more important to most ferret people is where ferret nutrition
echoes a badly needing and growing field of human nutritional studies:
geriatric nutrition and nutrition for specific health needs.  Unless the
elderly of a population are essential to the survival of many of the
young there is no reason to assume that a wild diet optimizes anything
for the health of those who are past breeding years.  It might, but it
can't be assumed to do so.  Nor is there reason to assume that a wild
diet is optimized for those with genetic vulnerabilities, and since
domestic ferrets in the U.S.  have a many generation history of being
bred to optimize appearance rather than health or longevity (Fancies
originally brought in more money.) it is possible to find that such
domestics can have dietary or health needs which differ from the wild
ancestors due to accrued vulnerabilities.
 
Similarly, there are knowledge gaps in the feeding of kibbled diets and
in the feeding of homemade diets.  These aren't anyone's fault of
anything of that kind, so no one needs to feel even a smattering of guilt
if what data currently exists is used but isn't perfect.  Perfection is
impossible, especially now.  We all simply do the best they can with the
current state of information.
 
Raw foods are natural and ferrets are not particularly prone to a number
of the illnesses from raw foods.  When they do get one of these, though
it can really be a whooper.
 
Working from _Biology and Diseases of the Ferret, second edition_
339 -341 Salmonellosis, "a gram-negative bacterium which can be isolated
on selective enteric media from infected tissues and feces".  In a 9
month study 5 species of these genus were found to be able to infect
ferrets.  I do not know how many of these also infect dogs, cats, and
humans.  Here is a description on page 341 of _Biology and Diseases of
the Ferret, second edition_ : Day One: lassitude, anorexia, and muscular
trembling, Day Two: bloody feces, Day Three: death, and accompanying
signs may include: dehydration, anorexia, moderately elevated
temperature, pale muscus membranes and malaise.  Temperature can
fluctuate.  Conjuntivitis may be present.  Miscarriage can occur.  (In
pers. com. Dr. Bruce Williams has added that fetid feces rather than
bloody ones are more likely.  To treat this the bacterium needs to be
isolated and tested for antibiotic sensitivity because many strains are
antibiotic resistant.  Hydration and electrolyte management are essential
for survival.  Glucosteroids and blood therapy may be needed.  There are
multiple past posts in archives of vets who have treated this in ferrets
who refer to it as very hard to deal with successfully.
[Posted in FML issue 4777]