Most of the body's natural way of generating energy involves turning macronutrients into glucose and later into ATP. sucrose and fructose just so happen to have very short and very fast routes to conversion.
That fast path is what I think makes sugar particularly problematic (as well as honey and a whole lot of other "natural" sweeteners that are just repackaged *oses). That big jolt of energy which the body ends up converting to fat since it has nothing to do with it is (probably) where most of the problem lay.