You might not think the RPF / FPF distinction matters, but it's pretty clear that fandom as a whole is more willing to accept the latter rather than the former.

We've got at least one real-life serial killer in the tagset this year from a fictional canon (Ed Kemper, in "Mindhunter"), and there hasn't been an outpouring of controversy. So there's clearly a normative line there, even if you don't see it.