Apart from that, there may be whole grain carbs or refined carbs. We are supposed to use the whole grain carbs and avoid refined carbs and sugars, as they are healthier.

This is where you nailed it – good carb and bad ones. Those who lived before us fed mainly on good carbs in lieu of what is obtainable today.

Like you said, carb, as a source of energy is essential in our diets, however, we can be fine without it because fatty acid is equally an alternative source of energy.

And yes, those who are obese ought to avoid carbs as much as they can. While glucose won't directly make you fat, it causes a spike on the insulin level which will lead to the relegation of fatty acid. Consequently, the body will create more cells to store the fatty acid. The cells keep growing bigger and bigger, and so will you.