Climate change, poaching, and introducing new non native species are just some of the ways we have endangered species. Grizzly bears can survive on their own, but over hunting has caused them to become endangered. Rhinos can survive on their own, but because they were born with valuable horns meant that they would be killed off until there are none left. It is not all natures natural course. It is us. And we need to conserve and save what we have hurt.
To de-extinct animals such as dinosaurs, mammoths and saber-toothed tigers is wrong on several levels; firstly, nature wiped out these animals countless years ago, so they are extinct for a reason. They had their chance. Second, we cannot possibly know anything about an extinct ecosystem, so it would be arrogant to assume we can control it. What would be the purpose of de-extincting animals such as dinosaurs?