I agree and disagree. There's nothing stopping people treating anything as a parody, but if the author writes unironically, it literally isn't a parody. I could be hyperbolic and say "we could treat mein kampf as parody, doesn't mean it is", but I think I can find a more contemporary example without having to resort to Godwin's Law.

American Psycho was written as a parody, and is interpreted as such, but the author has admitted that Bateman was a self insert for his own frustration with women and fitting in as a 27 year old (the same age as the character). Its a fascinating character study, but it still bears mentioning that the person who wrote it was fucked in the head. So yes, I don't disagree that a parody can be dissociated from the author, but it also needs to be said that sometimes, people with deeply misanthropic views use parody as a veneer to say what vitriolic opinions they hold while using that veneer as a shield to escape criticism of their strange and disturbing views.