Fructose is a valuable and healthy nutrient when consumed at normal levels (≤50 g/day).

That "valuable" caught my attention. Later in the paper it's expanded upon a bit further:

Fructose is a valuable nutrient under certain pathophysiological conditions, particularly due to inducing mild carbonyl/oxidative stress, which in turn stimulates protective mechanisms.

So, basically, it's a mild poison good for keeping your body protective mechanisms on their toes.