[adrian_b]

You are right, but this is a very specific circumstance when the required power output is so high that it exceeds the capacity of the intestine for glucose absorption.

As you say, in order to achieve the maximum power output that can be sustained for a long time, i.e. in aerobic effort, you also need fructose, i.e. sugar, besides glucose, to reach the maximum rate of carbohydrate absorption in the intestine.

However the vast majority of the humans may never encounter during their entire lives a circumstance when they need to produce a sustained power output so high that it is limited by the intestinal absorption (and without an appropriate training their muscles would not be able to sustain so much power anyway), so they never need to eat sugar. They eat it only because it tastes good.