I feel as if the fandom hive mind tends to understand things that can go wrong quickly (using epithets coming to mind immediately), and then writing advice swings to the black-and-white prohibition, as much writing advice does.

Good point, I agree this is a factor. I think many fan writers have anxieties about "doing it wrong", and when it's mentioned that some writing technique isn't the easiest to do well, people can feel safer just never trying it at all.