What generally a parasite is? It is a living being that takes food from host, in some cases, damages it and spreads itself exponentially.
Human, my dear reader, is a parasite; a giant parasite. Until a couple of centuries ago, we were living in accord with the nature: nature provided, we consumed and grew. Both nature and man doing what they were supposed to do. Then it occurred to man that it wasn't fun enough. Centuries of this accord looked like boring food chain span. "Why not just ruin the nature? That should be fun", man thought one day, about two centuries ago. So, a never stopping process of ruining nature started. Man invented machines, chemicals, electricity, bombs, computers etc. All equally lethal to the nature. Now the silent and providing nature didn't protest, in fact, it kept providing things that man kept turning against it. Two centuries later, turns out that damaging nature is actually killing yourself. We were always parasites: always getting, never paying back. But only now we have turned into poisonous parasites: paying back in lethal products.
I hope it's not too late already to save the nature, and to save ourselves.
If someone tells you that man is "The Greatest Creature of All", please assume that someone as the greatest moron.