I started telling him a story about how when I was a little boy, I'd spend my time running around outside playing war games. It was always the Russians against the Nazis. Long negotiations would always ensue about who got to be the Nazis, since everyone wanted to be the good guys. Since WWII movies were a staple on television and in the theaters when I was growing up, we all knew how to play the game. The Germans would scream "Schneller!" and "Hande Hoch!"; we ran around shooting each other, capturing prisoners, tending to the wounded.
My son asked how many Russians were killed in WWII. I told him - twenty million. He asked how many Jews; I told him - about a million. I told him before about the anti-semitism in Russia and so he asked me if the Russians helped the Germans kill Jews. I said, yes, but also some Russians helped Jews as well. I told him that just like all people there were good Russians and bad Russians, good Germans and bad Germans, good Jews and bad Jews.
It was then he looked at me and said, "Daddy, wouldn't it be great if there were no bad people in the world? Then you wouldn't have to worry about talking to strangers, or going outside by yourself, or locking the doors at night."