To me, it seems that we focus on the bad because the good isn't always so interesting, or perhaps because the good is already covered by an entire community of individuals with the future of the world in mind (we call them folks "scientists"). Maybe the bad is just that much more entertaining to write. For me, this is definitely true. It has something to do with beating up on my characters; I find something entertaining in torturing them. Maybe there is something similar going on with more well-established authors than myself. I don't know.
What do you think are the reasons why there is such a strong focus on the pessimistic in science fiction? Why is the optimistic not as appreciated? I'd like to know what you all think.