Bonobos are one of Earth's most intelligent species, and seem much kinder than humans.

Do they now? Looking at the Wikipedia page you linked to...

De Waal has warned of the danger of romanticizing bonobos: "All animals are competitive by nature and cooperative only under specific circumstances" and that "when first writing about their behaviour, I spoke of 'sex for peace' precisely because bonobos had plenty of conflicts. There would obviously be no need for peacemaking if they lived in perfect harmony." ... bonobos kill monkeys for food. For the biologist, this fact is irrelevant in any discussion of aggression and peacefulness, because it is predation (due to hunger, not aggression) practiced against a different species. Hohmann and Surbeck published in 2008 that bonobos sometimes do hunt monkey species. Five incidents were observed in a group of bonobos in Salonga National Park, which seemed to reflect deliberate cooperative hunting. On three occasions, the hunt was successful, and infant monkeys were captured and eaten.