The article mentions a 900-ton pile of mango detritus. Exactly how many mango skins and seeds a day would you be willing to eat? (They contain urushiol which causes blisters. Don't eat any!)

But that's just one part of it: this turns waste product into food. Beans don't provide complete amino acids. I don't know if maggots do, but many types of animal flesh do.

Also, most people crave diversity in their diets. How long are you willing to live on an all-bean diet, even if we make it nutritionally complete? Diversity in diet is ideal for humans.