Even if we were to apply thousands of years of selection and removal of violent people from our society, our society would still be violent.
Why?
History tells us that in times of peace, humans start to slowly group and turn against each other. We see this literally everywhere.
People at work are talking bad things against each other.
Why are they doing that? Is it because they want peace? No. It is because they have the need to degrade others and to fight.
This need to demonstrate superiority (which they all have) is what produces the conflict.
Verbal conflict escalates into violence. If one side seems "right" in the conflict, that is irrelevant. All sides are eager for the conflict.
"The early human tribes fought each other" not because of "some injustice that one did to other".
In fact, we see that throughout history people were eager for conflict and basically just waited for the excuse to do it.
The church supported the crusades. Muslims supported endless wars for islam. Germans supported Hitler. Russians supported Stalin. Americans supported Bush. Japanese supported their emperor.
Entire human history is a history of wars and conflicts and people manufacturing the conflicts.
People cannot possibly function without a conflict, as the people cannot function without disagreement and disagreement always leads to conflict.
Some people might say "peace is possible". However, peace doesnt exist in any society today, and it did not exist in any society before. Therefore, we have no reason to believe that peace is possible.
Even peace with nature is not possible, since humans have the compulsive need to destroy nature.
Humans cannot live without killing something and reproducing to the point of where population is unsustainable.
Even societies that seem peaceful from the distance are actually full of internal conflicts and people there are stepping on each other all the time.
There can be "little less violence", but there cannot be "no violence".
Kim Jong il believed that only a society with single-minded unity can be a peaceful society. If disagreement doesnt exist, neither does conflict. However, even when all people agreed on some principles, there were still disagreements on other things and violence was still present.