Why is sugar harmful for diabetics?

Sugar is a form of Carbohydrate - it contains (Glucose + Fructose) both of these are easily digest able; but since in diabetics there is lack of the harmone known as - insulin - this glucose doesn't converts to energy but rather escapes in blood; thus there is instant increase in the amount of blood sugar. this increase in sugar content of blood is the major culprit causing damages to the different organs of our body.