Working our way around the edges of the "real-world science" category, there doesn't seem to be a discussion about crackpot and pseudoscientific ideas.
There are a couple of near misses on Meta:
- Are speculative science questions on-topic?
- Are stories that only appear to contain fantastical elements on topic?
I would certainly agree that writings about crackpot theories presented as scientific truth are decidedly off-topic. But if a writing which hinged on the same elements was presented as fiction, we'd probably consider it as fantasy, science fiction, or some blending of the two.
- Rudy Rucker's 1990 novel The Hollow Earth would be on topic.
- Philip K. Dick frequently trod the line between SF and non-SF. His novel The Man Whose Teeth Were All Exactly Alike involves a semi-hoax involving "recent Neanderthal fossils" and is probably off topic since it only appears to contain SF elements (but doesn't really). But what if he had instead written them as real?
- A peculiar case is Zecharia Sitchin whose writings promoted "ancient aliens" theories. Eventually, however, he (or his publisher) decided to present them as fiction (see this answer of mine on Mythology SE). Is it SF if the publisher overrules the author?
If I think of more edge cases, I'll add them.