You can eat a little fruit once in a while, but it actually isn't important for your health. Think of it as natural candy. Now, vegetables/greens are important.

Looking through history, humans only had fruit available a few months/weeks of the year. Nowadays we can get all the fruit we want.

How are vegetables important? They provide little to no energy.

That's why they are important. :) On a serious note, there is nutrient density.

http://en.wikipedia.org/wiki/Nutrient_density

Most commonly, nutrient density is defined as a ratio of nutrient content to the total energy content. Nutrient-dense food is opposite to energy-dense food (also called "empty calorie" food). [...] Fruits and vegetables are the nutrient-dense foods, while products containing added sugars, processed cereals, and alcohol are not.

This is why replacing added sugar with anything that contains at least some vitamins and/or minerals is beneficial.

Fruit is actually a poor source of fructose. There's too much fiber, it can't be absorbed quickly.

Compare that to cola, which adds salt and bubbles so your mouth can't even taste how much sugar/HCFS it's swallowing.