Yes, and yet there are ancient tribes who have maintained their solidarity and culture for thousands of years. Competition happens. Raids happen. They some times kill each other. But rarely do they break homeostasis because they integrate all aspects of living, including illness and death.
No species does this quite like the modern human - not even other humans.
Okey, then I can say the same thing about viruses Sprinkles. They live in harmony etc. They live in harmony with our immune system etc. etc.
But take the immune system out and you'd be dead in days. The fact that the two are able to live together does not change the fact that they are in a struggle for resources. mixing cooperation with competition is just, human nature. It's how we compete against the environment with heightened in-species/in-group cooperation. competition is still there however.
These people are, on average, probably not deep thinkers about the long ranging consequences of each action (and even that is just delayed self interest, with the self identifying itself with its in-group to a point and common interests etc.) their system evolved to a certain degree of stability because they wouldnt be here otherwise. but it did not set itself free of its limitations, they are like these bacteria in our bodies which have their perks and their cons.
You know what happens when you give guns to primitive societies? They shoot the hell out of each other. The world is beautiful enough as it is without needing to defend lost causes. It's not progress for the sake of progress, it's what made you and me, it's the systematical adaptation of life to its environment. Most small isolated cultures are still there because they are isolated. It is also why they havent changed much in hundreds or thousands of years, lack of competition or interest from the competition.
They are the societal equivalent of a kid taught about life by hippies in a farm somewhere and then facing the rest of the world, where people are more educated, more connected, more effective and productive as a group.
We can argue subjectivity all day, fair enough. That's why I like statistics. If smaller societies with groups the size of what humanity's brains pretty much evolved to empathize with and relate to have higher homicid rate (much, higher) on average than even the homicidal maniacs amongst the developed countries (ie: USA) where individuals are so numerous there is a thousand ways to consider people living next door as 'out of your in group' and cut them off from your empathy lifelink. it kind of says it all. doesnt it.