When you knock someone down, how do you feel?
Probably, you feel good only “at the time”
“It was his fault, the bad one was him.” You may think like that.
But later, what do you feel? 
Maybe you are regretting. Right? 
“Why did I do that.” You may think like that.
It is just my opinion, but I think when people are doing something bad, the people aren’t thinking anything about the thing that will happen after the people do something bad.
I can’t do that if I think about the thing that will happen after I do it.
I’m afraid about that happen. I could go to jail.
But people who include me sometime knock someone down even though we understand what will happen then. I think it means when people knock someone down, the people don’t think anything. They are just according to their feelings when they are doing it.

 Usually we can control ourselves. So we don’t knock somebody down with no reason or few reasons. We can hold down our feelings. But it isn’t only good thing. Because of we can hold down our feeling, we explode. We suddenly do something wrong.
When various feelings accumulate and accumulate, people kill people.
What do you think about that? This is just my opinion though.
If human can’t control their feelings, what would happen?
It would be awful, because people do thing whatever they want.
If they can’t do something that they want, they would scream and rage as like as little child. Slugging match might be an everyday experience.
But I don’t think this world has homicide, because stress doesn't exist there, they don’t have to hold down their feelings there.
Little children don’t kill someone. Same thing.
They don’t have enough stress to kill someone.
If human can’t control their feelings, black feelings would disappear before they kill someone.

 Human is the only one animal that has reason. We can think, we can control ourselves and we can communicate with someone accurately. But we are still animal. We are not perfect, so when your feelings accumulate and accumulate, you explode, knock someone down and kill someone. When the limit of endurance comes, human is according to instinct to save himself. If human exceeds the limit of endurance, they would break. So people are being mental illness. The world that I showed you before, of course I know that can’t be real, because if so human would be animal just like as dog or something. We can’t have advanced intelligence in that world, because in that world people lost reason, it also means they lost intelligence. Do you think they can communicate with someone? I don’t think so, because if you are discussing with them and you said contrary opinion. They would not talk to you anymore unless it become as they said.
So they may lose language. They don’t need it. They will become wild animal.
But which world is happier to be back to wild animal or to have advanced intelligence?  
I don’t know.