The majority of folks will do better an a mixed diet, containing some form of carbohydrate.
Now the true issue with carbohydrates is not so much the presence of carbohydrates, but the quality and quantity of carbohydrates consumed.
Portion sizes cannot be ignored here. The majority of layfolk simple eat too many carbohydrates - and probably less than optimal choice carbohydratres - in one sitting. Take pasta, for example. How many people typically will eat a modest portion size at a meal? Say a few tablepsoons.... not many.
People pile their plates full! Similarly, not all carbohydrates are created equal. A carbohydrate obtained from a tuber, or a soaked grain / legume, is very different from the frankenstein foods we typically come across in the supermarket.
Couple the fact that people overconsume poor quality, highly processed junk - with inactive lifetsyles - then yes, health problems and poor bodycomposition result.
However, good quality, appropriately timed foods, in the right amounts depending on individual's goals, coupled with a decent volume of high intensity exercise, results in favourable metabolic and body composition adaptations.
The quantity of carbs depends on what you want to achieve, fat loss or muscle gain.