The problem with Sugar is ….

Sugar contains no essential nutrients and is said to be bad for your teeth. Basically, you are adding empty calories.
Sugar causes tooth decay by feeding the harmful bacteria in the mouth.

Added sugar is high in fructose, which can overload your liver. In some cases, it may cause non-alcoholic fatty liver disease.

Sugar can also cause insulin resistance, which can further lead to metabolic syndrome and diabetes.
Sugar is highly addictive; it may cause massive dopamine release in the brain.

Sugar is one of the leading contributors to obesity, both in children and adults.
But it does not mean that you should avoid sugar completely. But it should be taken in a different form.