World has not learnt lessons of Holocaust

Why do human beings always learn the wrong things, to cheat , to steal, to kill. But never in this while, a human being could turn wise enough to learn the greatness of helping each other, to share and to forgive. From the recent reports about the mass murders in cambodia and elsewhere, it had just proven once again that men never learns from history or their mistakes but stubbonly repeats them.

Is it true that " All that is needed for evil to triumph is that good men do nothing"? I believe evil would seize to exist even when the good men does something. Similar to police and crimes. Even if there are multiple or lots of crime preventor taking action each time to stop crimes, they still do take place. Take terrorism and the law enforcer as an example, this is a cycle that could never be destroyed because the terrorist refuses to change or give up on their attempts of hurting others because they felt indebted to take revenge for the close ones who died. Perhaps, the problem lies in forgiving one another. There is a saying that it is easy to forget but never easy to forgive. Therefore, in my opinion, stopping the action of mass murders by force isn't enough.