Why do we do it?

I want to write because in my own stories you can make what I want happen! If anyone ever asked my suggestion about how write, that would be mine: think of something you would really hate to happen, and write a story in which it was prevented, with your central characters being the ones involved. That way you feel committed to the story and the characters. That might seem obvious, but when I tried taking creative writing courses, they seemed to centre on what you could sell rather than what you felt strongly about. In a way, that is realism, but it seemed to me to involve a certain cynicism, as well. So I wrote what I wanted to.
If you read about the myths and cultures of the world, you come across some odd stimuli, or starting points from which to start writing. I was reading about the ancient Norse people, the Vikings. They believed in a certain type of ghost, that of an unwanted child that had been left out in the snow to die. This ghost would sometimes come back to seek vengeance on the parents who abandoned it. After reading that, I wanted to write a story in which someone found these abandoned children and took them in. I got down to it, and the result was a novel that I titled "Outcasts of Skagaray."
Other things could prompt the same feeling. I heard somewhere that the two young gunmen who carried out the Columbine High School massacre considered some people 'not fit to live.' The same attitude was true of the boy who carried out the shooting at the school in Finland. There have been some horrors of history carried out because of that sort of attitude. The Nazis who ruled Germany for part of the Twentieth Century acted on the same notion. So did the scientists or officials behind the Lynchburg Experiment in the U.S. at about the same time in history. Then back in ealier times the Romans used to discard children they considered weak. Human history is full of cruelty. But sometimes there are good outcomes. There have to be, or life could not be worth living! And sometimes creative fiction can show what might be possible, what can happen if only.....
So we keep writing. We might inspire others to keep hope and faith. Any ideas?