Dolphins and killer whales are capable of all the things you describe. So are all great apes. Chimpanzees are capable of genocide. It’s not even human nature. It’s just nature.

Are you familiar with Dunbar’s number? The problem isn’t how people organize, it’s how many people organize. You get groups too big, the human empathy module short circuits and starts ignoring other humans as such…

You know what other animals can organize in large collaborative groups and not fight each other? Ants, bees and mole rats. Eusocial animals.

The problem with eusocial animals is they divide into genetically determined castes… So nature has shown us it’s either small packs or become a drone for the hive, and the problem with small pack is that larger packs destroy them.