Wild animals face disease, predation, parasitism, and starvation on a massive scale; understanding this challenges the assumption that wild life is inherently good for animals.
The assumption that wild animals live in harmony is contradicted by evidence of widespread suffering from natural causes. R-selected species that produce many offspring suffer enormous infant mortality. Disease causes prolonged suffering in individual animals. Predation involves terror and physical trauma. This does not mean nature should be eliminated, but it does mean that wild animal welfare is a genuine ethical concern beyond just human-caused harms.