If you add both good and bad you are producing waste. Tree is symbol of production/reproduction, hence "tree of good and bad" would mean humanity (original Hebrew word is Adam) chose a path of wastefulness after leading a perfect life on a perfect earth for a sufficiently long period. Hence what we find is the wasted earth, not the original, perfect earth. Because what happens to your body is the manifestation of what is going on in your internal world--mind, and similarly, earth too would change after humans change their paths on to wastefulness.
For example, last year during my vacation time I purchased one German Shepherd when it was a baby, and I fed it for less than two months, and returned to my College. After one year again when I visited my family, when I got down from the taxi itself, this now-gown up dog was trying to break its chain to come towards me to show its love. My dad released the dog, it came running towards me, stood up with both the hands on my shoulders--with my nose touching its nose. What a deep expression of affection from a dog just because I cared for it one year back, when it was a baby!
If humanity had done the same with all the other animals, we would not have had carnivorous ones, all--humans and animals--would have lived as one family. Even carnivorous one, if it is removed from its community when it is a baby and allowed to grow with lambs, it will return to lamb's nature.
But humanity's purpose is changed! We started the sports called hunting the animals, began eating them. Our purpose is to accumulate exceedingly to create privation in others, and enjoy seeing others suffering. (https://www.theguardian.com/global-development/2017/jan/16/worlds-eight-richest-people-have-same-wealth-as-poorest-50)
Following such mentality is what eating from "tree of good and bad" means.