We have become experts at wiping out species that took millions of years to evolve. Humans are just one species to share this planet. We have always displaced plants and animals with our development, but now we are doing at an accelerating pace. Killing of lions upsets the balance in the African ecosystem, accelerating the decline of other species and ecosystems.

If you want a purely selfish answer, humans won't last long on this planet if we continue to abuse and distort the environment. There are precious few planets in the Universe with life. So few that we have yet to encounter another one.