Lots of answers to this question but I am focusing on one particular thing. The natural world is a constant struggle of all against all, but this struggle is quite different from the worldwide violence that humans have created. What is different about natural vs. human struggle?
The struggle for existence in nature can sometimes be very violent, and can (especially for victims of parasites) gruesome. But usually what you see in nature is a struggle that can be called “I will outgrow you” or “I will out-reproduce you” or “I can do better than you” rather than “I will kill you.” Natural selection, the engine of evolution, is not always bloody; it is competition.
Consider a forest. You look all around you, and you see green leaves. If you look closely, and at the right time, you will also see herbivores such as caterpillars. The leaves produce toxins, and the caterpillars tolerate them, resulting in a balance that ends up, by chance rather than by design, allowing both of them to survive and even flourish. This is struggle for existence but not violence. You can feel peace in a forest but not, of course, on a battlefield or the scene of an ISIS terrorist attack.
In contrast, you cannot hear a single day of news without being confronted with violence, sometimes unspeakable violence, all around the world. Humans, perhaps uniquely among all species, have gone far beyond the Darwinian struggle for existence and gone into what can only be described as evil. Humans, unlike other animal species, are not content with simply out-competing another person. In this sense, the religious people might turn out to be right, that humans, alone among species, are fallen.