To me the carb debate has to be split into two areas, call them the Pre and Post Type 2 Diabetes arenas
In the pre diabetes arena you are really arguing if increasing carbohydrate intake can account for the increasing rates of obesity as Type 2 diabetes is just one of the many disorders that can happen because of obesity. So for example there is a known relationship between "getting something nasty" and BMI. Look here for what WHO says
http://www.who.int/nutrition/topics/5_population_nutrient/en/index5.html The same page details a similar link between simple waist measurement and "getting something nasty"
Given the ratio between carbs / fat / protiein has done significantly different things in different countries over the last 50 years ago yet in those countries rates of obesity and Type 2 have all risen then my opinion is in general terms a particular diets amount of carbohydrate intake has little to do with whether you end up as Type 2 unless it's a blatantly wacko high calorie one as well.
What seems to be the cause in my opinion is simply the energy density (eg number of calories) people are consuming. So perhaps its only in the last 50 years that ENOUGH people have had the opportunity to eat dangerously high calorific diets to actually reflect it in the underlying statistics. Also that the calorific "damage" of what people eat is then magnified considerably by modern society's lack of activity and exercise etc.
Again look at the table in this page
http://www.who.int/nutrition/topics/5_population_nutrient/en/index3.html for factors that WHO think promote or protect against obesity.
Once you've got Type 2 then the whole debate changes in my opinion. There seems to be little doubt in my mind that there is (or will be proved) a causal link between carbohydrate intake and long term survivability and I currently make a personal choice each day to say a low carb diet is my best option for my survivability.
However I would argue that what I think is best for me is by no means best for everyone and no one diet be it ultra low, or low, or medium, or high in carbs is any better than any other one. Under all these scenarios a diabetic can make an informed individual choice as to how they wish to treat their condition. Some (like me) can effectively go for low carb and little meds others can choose high carb and insulin.
In my opinion the important bit is this; so long as in both those examples those people choose the correct energy density for their style (i.e the right calorific amounts to keep them fit and healthy) then the choice of low or high or whatever carb seems pretty irrelevant to me.
In my own case I choose a 65g / day low carb diet because I get safe BG's at that level. There is nothing stopping me wanting to go ULC if I want to and say stop my Metformin or decide to quadruple it and go on insulin. The only unevenness in the choice is that I could go ULC as a plain life style choice but so could any non diabetic as well. What I can't choose is a high carb diet unless I'm prepared to take the meds or insulin to allow it.