This is a naive viewpoint I see pop up a lot. People pushing "fiction" think it's a "fact" and there's no full-proof way to convince them otherwise or even perfectly distinguish the two. People will tell you that it's a fact that vaccines cause autism or Iraq has WMDs or America is a white supremacist country. In reality, "facts" are linguistic simplifications of reality that inherently omit information and the distinction of "fact" from "fiction" is itself a simplistic way to attempt to describe the accuracy of a statement. On a personal note, the people most convinced that they are pushing facts are the ones I'm most skeptical of.