Fructose can be more harmful than glucose for a couple of reasons...
When glucose enters the bloodstream it is regulated by insulin but fructose is processed by the liver. The liver can't process too much so it turns it to fat and sends it into the bloodstream as a trigylceride. This in turn can result in liver disease, heart disease, insulin resistance and type two diabetes.
High fructose diets also contribute to weight gain because they bypass hormonal controls which tell your body you are satisfied when eating.