I just have to say, "A Canticle for Leibowitz" shook me for a really, really long time afterwards. I'm not saying it's a bad book, it's quite thought provoking, but I took about 99 points of psychic damage from it.
As to the bleak outlook, I don't remember enough (it was a long time ago), but a few years ago looked it up on Wikipedia https://en.wikipedia.org/wiki/A_Canticle_for_Leibowitz?usesk... https://en.wikipedia.org/wiki/Walter_M._Miller_Jr.?useskin=v... I learned that Arthur Miller Jr suffered from depression and chose to end his life with a firearm in 1996, age 72. I am always somewhat 'on guard' when I read works from people who were suffering with an illness like that, wondering how much of the story is infused with unnecessarily dour material when another, perhaps more upbeat approach, would have served the story as well. I guess I do not want to be dragged into depression by being overly bummed out by Fiction.