If we abandoned the planet tomorrow the earth would repair itself and there would be peace and harmony in Nature.........
As nice as that sounds, it is a lie to believe nature lives in harmony. In earth's history, more species have gone extinct than exist on the earth today. Regardless of the changes man has made... nature has never been anything but a war for survival. Lions and bears are not 'in harmony' with the species they hunt. Predators were hunting prey to extinction long before man came along. This is fact, demonstratable by the fossil record.
It's silly to consider the works of man 'unnatural'. Everything in nature is a product of nature, and that includes man and his behavior. Man takes every advantage it can of it's environment the way all species try to do. Ants and bees build colonies. Beavers build dams. All species have an impact on the environment they live in, positive and negative. Man just adapts his environment to suit his own needs really, really well.
Sometimes even man is at the mercy of natural creatures changing their environment. The bacteria that grows in your gut produce chemicals that trick your immune system. They change YOU so that your own immune system fights off bacteria that are their rivals - sometimes causing food alergies.
Man does some unfortuately distructive things - but unlike a beaver that wipes out a species of frog by building dams in an area - humans can recognize the damage they cause and make an effort to reduce their impact.
- Lime