"Satire doesn't stand a chance against reality anymore."
— Jules Feiffer in 1959
The core idea of Poe's law is that a parody of something extreme can be mistaken for the real thing, and if a real thing sounds extreme enough, it can be mistaken for a parody (all because parodies are intrinsically extreme, in case you haven't noticed it). This can also happen to someone whose picture of the opposing position is such a grotesque caricature that it renders them unable to tell parody from reality. Reality and parody are further blended by the fact that something that started as a parody might turn into a Windmill Political that some people take as gospel and go to a very serious (if not literal) war.