CathInfo.com

This debate is based on perspective/goals.  If you're living a sedentary lifestyle, then you don't need many carbs and keto/paleo is your best bet.  If you're trying to get in shape and workout 5x a week, with cardio/weights, then you need extra carbs.  Sugar can be a % of those carbs; plain sugar has been used by weightlifters for decades.

Ask any weightlifter who is doing keto.  They will tell you that their cardio stamina dramatically falls, due to low glycogen in the blood.  But they typically don't have problems with lifting weights or losing strength. 

On the other spectrum, look at high-endurance athletes who train for marathons or Ironman competitions...their diet is mostly carbs, because they need to replenish the glucose which they burn through due to high-cardio.

Bottomline:  Your diet depends on what your exercise level/goals are. 
-  A keto/low-carb diet can provide muscle gains, but your cardio stamina will be horrible.
-  A high-carb diet will provide the best cardio/endurance performance, but muscle gains will be smaller.
-  For sedentary people, a keto/low-carb diet, with mild exercise, will have the best results.

If you don't exercise at all, your body will get used to any diet and your insulin levels will suffer.  Exercise is essential (even a 30 min walk, 4x a week, can have surprising benefits to fat loss).  Choose a diet based on your exercise goals.