I want to reply specifically to your question:
is there some specific kind of literature, some author, some writing style, some period, some subject matter, some language, that bring some toxic memories?
Yes - interestingly, the topic is “learning a foreign language.” I got a little bit of instruction in French in 1st grade and loved it. How interesting that other people used different words for the same things! I liked learning new words, and now there were more of them!
However there was no language instruction in my school after 1st grade. I don’t know why, maybe French had just been an interest of that particular teacher. I didn’t study a language again until 9th grade. This was a horrible school year, and I hated everything I studied then. Fortunately, I had outside learning that interested me in several areas, but not in language. The only language instruction I had was in school, and the main experience was of struggling to memorize lessons, being discouraged by how quickly they were forgotten, demoralized by my slow pace in comparison to the seemingly infinitude of the task. I tried again a few times later, and never made progress. Lack of other language was a handicap in the rest of my studies, but was never able to overcome my dislike of the process.
That experience is actually the root my reading your essays for the first time. Almost miraculously, thanks to a fellowship from the Knight Foundation, I had a chance to return to school in my mid-forties. I had just 9 months, but I could study anything I wanted. I was at a big, famous university where there were many advanced courses to explore, but nobody was telling me what to do so I took what I thought might be my last chance, and signed up for a first year Spanish course. I remembered how discouraging it had been to forget the vocabulary I’d memorized in my other attempts, so I searched on the Internet for a digital flashcard program I could use on my Palm Pilot III.
I found something about spaced repetition and Supermemo in that very first search, downloaded the program, and was finally on my way. Some of my colleagues from Spanish speaking countries were astounded by my sudden ability to communicate with them using my terrible grammar and seemingly random collection of words (After the first three months of memorizing basics, I started looking at articles in the newspaper and memorizing whatever I didn’t know, which meant for some odd vocabulary.) What a pleasure it was to finally succeed.
So, yes! I had this experience. I also have toxic memories of trigonometric functions. Although I got into college coursework in math, and liked topics in algebra and number theory, I was never able to make progress in analysis because the geometric functions were gibberish to me. I always had to look them up, never had a good intuitive sense, and even doing simple calculations, if some kind of trigonometric substitution was required I had to grind my way through. How embarrassing this is today. And guess what: Trigonometry was also a 9th grade class. It’s like a bomb went off in my brain that year, and any subjects that were emphasized then became radioactive.
I think I know why you ask this question: You want to argue that the most important thing is to know when what we are doing educationally is setting off radioactive bombs, and – even if we do nothing else – at least stop doing this. You also want to argue that the sign of a ticking bomb is simply resistance and lack of pleasure. You say not just learning can be fun but learning must be fun.