Evolution kills entire species all the time (on a longer timescale). Humans kill them much faster. But the planet doesn't care. A mass extinction is just a footnote in history; something for future species to dig up traces from. Life will survive whatever we humans can do to our planet. Even a full scale nuclear war lacks the capacity to entirely sterilize this little blue sphere.
Of course we feel sad about polar bears, tigers, elephants, and pretty much all coral reefs and fish dying. We have empathy. That's part of the human condition. So we cry out about "saving the planet".
Nature has no empathy. If nature can be ascribed any sort of intent or personality it would be that of a particularly cruel sadist. Drop a giant meteorite in the Americas to kill 98 per cent of all life on the planet? Why not? Ice age? Fair dues! We only cry about the poor planet because enough rodents have survived previous mass extinctions for us to descend from them. It's not about saving the planet, because quite frankly the planet doesn't give a shit and polar bears don't even understand the concept of extinction.
It's just that we're a species too, and we're a part of the same ecosystem as those fluffy white murderers. Maybe the death of polar bears won't change anything for us. Maybe the death of tigers or elephants won't either. But they're not the only ones we're killing, are they? And the more species that die the more our ecosystem will become unbalanced. We're putting ourselves in a very precarious spot, because we depend on that ecosystem. We don't have to save the planet. We may not even have to save the polar bears. But we do have to save ourselves, and the road to doing that is to preserve as much as possible because we simply don't know where that dangerous line we mustn't cross is.
And Earth sure as hell doesn't give a fuck.
-- CC0 Björn Wärmedal