I just wrote one last week, inspired by a scene from a science fiction novel. It tells the story of a small fleet of spaceships fleeing a doomed Earth for the stars, and one ship attacking the rest and killing their crews in order to steal their fuel and spare parts. It's not just that what they did is a crime... they knew it was wrong, did it anyway, and feel terrible about it, but they also knew that if they didn't do it, another ship would have done it to them. So it's all guilt and shame from making a totally selfish decision.
Why would I write that way? And it's not like this is an unusual subject for me.
Part of it, I think, is that I do a very good job of covering up some deep depression in my day-to-day life. I'm a much sadder person than I appear to be.