Sugar doesn't cause insulin resistance or (type 2) diabetes. Both are a result of being overweight.
Of course, you can get overweight by eating too much sugar, but it's really about not eating too many calories long-term, regardless of the source.
And of course, refined sugar isn't healthy at all and consumption should be kept to a minimum, outside of exercise.
Carbohydrates do cause insulin resistance and diabetes. India has average BMI of 21,9, yet has very high incidence of diabetes - largely thanks to its carbohydrate-based diet.
There are many people with type 2 diabetes that are not overweight; and also many people with overweight and even obesity who do not develop type 2 diabetes. The estimate is that around 537 million people have diabetes worldwide, while overweight and obesity is estimated to affect 1.1 billion people.