I still have my t-shirt that says "When in doubt, go to the library." It's soft and comfortable, it fits me perfectly, I like the sentiment and the design. And I have to get rid of it. Not because I think it's going to do anything to JK Rowling, who continues to rake money in with both claws, no doubt hissing happily. She will never know or care what I think of her.
But it's not for her. It's for my nephew.
He loved the Harry Potter books growing up, just as much as I did. He wrote fan letters to Rowling, thanking her for coming up with such a wonderful world. He came out as trans not long after Rowling went full TERF, and her attitude broke his heart.
At this point, if I wear Harry Potter-related merchandise of any kind in public, I know the message I am giving to the kinds of people Rowling thinks shouldn't exist. They can't know I'm a safe person if I choose to wear that shirt. And while Rowling's opinion doesn't matter to me, my nephew's feelings do.