fiction and non fictions - where do the lines lie and cross?

ive been getting into debates on X with a lot of ppl in the art community about the ethical and moral aspects of art, in particular the portrayal of heavy topics and how they should be handled (think heinous crimes) a lot of them use the line "its fiction so it doesn't matter" as a defence.

this has really made me think about where the lines of non fiction and fiction exist. and i personally feel that all fiction will have some elements of non fiction and don't believe its possible to create something that doesn't have any roots to something real. hence why the defence of its fiction is a poor one.

any thoughts. its my first time here so I'm sparing going to specific examples i used during the debates as they can be triggering however I can if needed.