Bitch modern humans have been on this earth for six hundred thousand years creating an enormous number of distinct and unique cultures which shape the people living under them. The absolute arrogance to think you can generalize a hundred billion people's worth of experience based on what you've experienced in your one tiny lifetime. Humans are so fucking diverse there is VERY little you can say is "human nature." But no please tell me more about how people are just selfish by default despite all the fucking evidence to the contrary.
It's so unfortunate that this view is drilled into us continuously throughout school, at least in the United States. I remember reading Lord of the Flies in high school and the class's main takeaway was that most humans, especially children, are just terrible in some fundamental way.
Meanwhile the actual Lord of the Flies kids did just fine until they were rescued.