“We” are the deadliest species of all. But you might know that already! Sweeping all those animals to extinction was crucial for our survival and we wouldn’t have survived at all if our ancestors would have done anything different from what they did (30,000 years ago).
The author paints quite a picture in the book, “Sapiens” on how we killed millions of species which inhabited the world before the cognitive revolution took place. It doesn’t look nice nowadays as it was brutal and inhuman. But the world back then wasn’t a nice place too, it was hostile and sparing those species meant risking our survival. They basically it what they had to do in order to survive.