I’ll go with the low-hanging fruit: Mein Kampf. I’ve read it, cover to cover. As a piece of propaganda, it’s good. As an example of good writing? Absolutely not (though I will admit I have only read it in translation). Oh, and the whole fascist, racist, and generally shitty worldview of the author that he infuses into the text. And the fact that the author is literally Hitler. You 5-star that book? You’re a Nazi. Period. And as a Jewish person, I don’t look too kindly on them.
At this point, any of the Harry Potter books.
I’m not gonna debate people on “separating the art from the artist” or anything. But even as someone who used to be a huge HP fan and still has a lot of nostalgia attached to it I’ll admit there’s much better fantasy out there.