I think that sugar in an otherwise healthy individual can be coped with. We can discount Type 1 diabetes being caused by sugar as it is due to an autoimmune attack. In individuals with a family history or genetic predisposition to insulin resistance, then sugar can be an accelerating factor by making the pancreas work harder, but it's not a cause - many other factors may accelerate the decline of the pancreas or increase in insulin resistance, so sugar may not be significant in many people. Also, there are many more people who consume vast amounts of sugar and don't become diabetic, so sugar can't be a cause otherwise they would all develop diabetes.
I'm sure someone can put it better than that, but I hope you can see what I mean! 🙂