I remember maybe 40 years ago reading a short science fiction story in which, in crowded cities, someone in a crowd would randomly go "berserker" and start killing everyone around them. I believe it was due to overcrowding from overpopulation. It was far out. But it was prescient—we are there, although the motivation may be a little different (or is it?). I wish I could remember the author or the name of the story. I'm pretty sure it was a short story, and not part of Soylent Green.