Five monkeys are in a room with a ladder in the middle. Hanging at the top is a bunch of bananas. Now one of the monkeys attempts to climb the ladder and all of the monkeys are sprayed with ice water and become miserable. The next time another monkey tries, they all gang up on and beat the crap out of that monkey.
One monkey is taken out and a new one joins. The new one, not knowing about the water, attempts to go for the bananas. He is quickly beaten up despite no one being sprayed with water.
Soon enough, all of the original monkeys are removed and new monkeys are present. None of these new monkeys have ever been sprayed with water, but whenever a new monkey is added and attempts to get the bananas, he is attacked and beaten. None of them know why, but just know that it is “bad”.
This is how most of the human race works – committing harm to other people for reasons that they never really understood in the first place.