How about this for a truth?
No one here knows what causes any form of diabetes, they just have a variety of theories based on scattered data overlayed with their own personal belief stream.
The answer lies in the "unknown unknown's" and to date they remain elusive.
When you apply the "But Why" to all of these theories you ultimately get down to a "We really don't know"
With regards to the study of metabolic processes we only find the things that we look for, new discoveries are generally accidental, how can you design a set of experiments to look for something when you don't know what it is.
Now with regard to the Metabolic Advantage Hypothesis, it seems evident there is no metabolic advantage with either of the energy macro's, there is merely differences in the way they are processed by the body which is determined by the body's current state of being and the way it sees fit to distribute it's fuel supply, overall carbs will build up fat stores just as well as fat does.