Even within the genre, people have very odd ideas sometimes.

I've lost count of the number of times a SFF reader has said "aliens = scifi" or "fantasy must have magic" or "fantasy can't have high technology" or "if it has time travel, it's scifi" etc etc. A lot of the differences between SF and F (such as they are) come down to presentation and tone. A lot of the differences between litfic and genre fic come down to presentation and tone. Actual ideas are very flexible things.