I don't understand how anyone can say a statement as heartless as "humans are cancer", but I shouldn't be surprised because it's within our nature to oversimplify, categorize, and put good and evil label on things. But the truth is that you can't put a label on humans because we are too diverse for that. For as cruel and heartless humans can be, we can also be kind and forgiving. There are millions who dedicated their lives in helping others, and millions of forest rangers defending what you label as good. You know that life has existed on earth for 3 billion years, so what good did it do exactly? Creatures born and died one after the other and what good did they ever do? Also life wasn't always stable on earth, there where 5 mass extincttions, and 5 ice ages long before we industrialized. It's been a few hundred years at most since we've been a "cancer" to earth. If humans where gone things will continue as normal, stars shine until they fade without anyone to gaze at their beauty. Universe will turn dark without anything happening. I don't think things will stay like this. Humans where hunter gatherers for ~288000 years but we grew out of it and learned to do better. I think the same will be true for war and injustice. We will grow out of these childish actions one day.