A good moral principle is ‘don’t do things that needlessly harm people’, but unintended consequences are everywhere. By delaying a passerby two seconds while you give a homeless guy $5, you might end up causing them to get hit by a garbage truck that would otherwise have missed them.
You can’t enforce the principle consistently, but that doesn’t make it worthless; you give it a good-faith, best-effort go, and that’s all you can do. If your best efforts turn out to be disastrous, that’s shitty, but life’s unfair like that.
Also, whatever else was going on with the person 800 years ago, JK is right now causing ongoing harm in her relentless campaign of hatred for trans people. Waving her IP around is promoting her cause, and so harming more people, right now.
If nobody knows whether the 800-years-ago guy was a piece of shit or not, then promoting their work isn’t supporting some piece-of-shit cause and harming people.
As for chicken sandwiches - without explaining why you think my analogy was inapt, calling it bullshit is no more of a slam-dunk rebuttal than if I called you a poopoohead.
Entity X makes product Y and does shitty horrible thing Z. By being a product-Y fanboi and promoting Y all over the internet, you’re expressing approval for X and condoning Z (at least enough to cut them slack for it).
What difference does it make whether Y is a media IP or a food product?