Why is fructose considered dietary?

Fructose is a simple carbohydrate, a monosaccharide, almost 2 times sweeter than sugar and slightly less caloric. It does not cause insulin spikes and its glycemic index is only 20 versus 75 for sugar! At first glance, this is an excellent property, and thanks to it, at one time it was believed that fructose was safe for diabetics. But it's not.