The Earth will be just fine without humans, the planet will definitely be better without us. The planet does not need us in the sense that we are not part of a larger, dependent ecosytem. We are not on the food chain.
Humans obviously have an awareness that others beings don't. We manifest things like hate, judgement, greed, vengeance, intolerance, spite etc. that animals (to my knowledge) lack.
We are completely to blame for our actions, and we should be held responsible when we kill other beings (or let them die). We can choose, unfortunately.
What if you could give those Yangtse dolphins a loaded gun? If that dolphin were a human, it might use that gun and threaten humans - let alone shoot - in order to preserve itself and its kind.