I feel similarly. However, I absolutely love Vonnegut, but don't see his work as scifi. Sure it has all the elements, but the themes are mostly different. To me the best scifi is about a technology that could exist and plays through all the consequences. Slaughterhouse Five isn't that, it's about WWII. (From my definition one might guess correctly that I see space opera as a derogatory term)
I heard that his writing could have been a way to process what he went through during the war. That could explain the darkness.
There is a modern fantasy writer that writes quite dark stories. I read that this is because of a very sick family member, and some of his best books have been written in a hospital room. While I applaude both for turning something bad into something good, these sort of books are just not my cup of tea. And I think a lot of people are like me. We read books to get away from the problems of real life, not dive into other people's troubled minds.
"And I think a lot of people are like me. We read books to get away from the problems of real life, not dive into other people's troubled minds."
That certainly makes sense and is of course also a subjective preference. To me great insights lie in the darkness, but it isn't for everyone and not at any time.
