If someone writes fan fiction making the pro-slavery and the anti-slavery sides of a conflict morally equivalent, or, worse, the pro-slavery side the good guys, and we choose to completely suspend judgement and shut our eyes to the implications there, that's a moral abdication. As Neil Peart wrote, "if you choose not to decide, you still have made a choice." Desmond Tutu had some words as well, about people who are neutral regarding injustice.
Your choice to take personal insult to a general point is your own. Your choice to assume the most hostile possible interpretation is your own. It's one I've seen you make a lot. Which is a bummer.
It's a big world, there are a lot of different types and degrees of depictions of unsavory content. I'm not saying that it's always an easy black and white line or that liking fiction with morally-dubious stuff in it is inherent immoral, by any means. But ignoring history and context rarely gets us anyplace good. If someone makes their Space Nazis or their Space Confederacy heroic, barring other data to the contrary, you can reasonably infer some things about their worldview. If they make their Space Federation one where
slavery is explicitly protected by interplanetary law, likewise.