I've been using this example for at least 10 years with econuts: fly across the U.S. during daylight hours and look out the window. Then honestly convince yourself that the human species is capable of destroying the entire global environment.
We are gnats by comparison to planet Earth.
Yes we are gnats, but we are almost 7 billion gnats. We ARE planet Earth. Perhaps for 10 years those econuts have laughed at what you said too. You think we haven't seriously altered the Earth already??? Most of it isn't anything bad, but really answer yourself this... fly across the US during daylight, and try to imagine what it would look like WITHOUT the human race down there. The plains would no longer have the characteristic quilt pattern, forest would cover from New York to South Carolina... and I mean COVER it. Forest forest forest forest, non stop. That's how it was when we arrived a few hundred years ago here. Drainage patterns, ecosystems, the atmosphere, etc etc, we have altered everything you can imagine and then some. Not that I am really complaining, just noting it. Read some of Carl Sagan's stuff, he was great at making those sort of illusions.