What Is It in Human Beings that Makes Them Want to Destroy Others?

From  the diary of Etty Hillesum:

19 February, 1942

What is it in human beings that makes them want to destroy others? Jan asked bitterly. I said, "Human beings you say, but remember that you're one yourself." And strangely enough he seemed to acquiesce, grumpy, gruff old Jan. "The rottenness of others is in us, too," I continued to preach at him. "I see no other solution than to turn inward and to root out all the rottenness there. I no longer believe that we can change anything in the world until we have first changed ourselves. And that seems to me to be the only lesson to be learned from this war, that we must look into ourselves and nowhere else." And Jan, who so unexpectedly agreed with everything I said, was approachable and interested and no longer proffered any of his hard-boiled social theories. Instead, he said, 'Yes, it's too easy to turn your hatred loose on the outside, to live for nothing but the moment of revenge. We must try to do without that." We stood here in the cold waiting for the tram, Jan with his great purple chilblained hands and his toothache. Our professors are in prison, another of Jan's friends has been killed, and there are many other sorrows, but all we said to each other was, "It is too easy to feel vindictive."

This is from the book, An Interrupted Life and Letters from Westerbork, by Etty Hillesum, p.150. Etty Hillesum was a secular, assimilated Jew living in Amsterdam who died in Auswitch in 1943. The diary was written after the Nazi occupation of the Netherlands, while the Nazis were persecuting the Jews and shipping them off to concentration camps. Etty had a degree in law and then studied Russian language and literature. On her own she read philosophy, psychology, especially, Carl Jung, and poetry, especially Rilke. She was a patient,  personal secretary, and physical intimate of the psychoanalyst Julius Spier, also a Jew. He introduced her to the gospels and the writings of St. Augustine. Etty had several opportunities to escape the Nazi persecution, Instead she insisted on serving her fellow Jews to the very end and chose to suffer the same fate as they. Her last letter was a postcard tossed from the window of the train as it left for the concentration camp.