I know it's frustrating, and no one is obliged to go out of their way to fix bigots, but compassion does work. An enormous amount of bigotry comes from a place of fear, and assuaging that fear leads to real change. It's not right to tear down the efforts of people who choose to do the emotional labour and put in the work, because what they do is incredibly valuable.
There's a balance to be found between the immediate need to shut down expressions of bigotry (especially because it's always bound up in fearmongering, and spreading fear spreads hate), and the long term eradication of bigoted worldviews held by individuals.
You're absolutely right that it's more important to protest a JKR booksigning and prevent it from happening than to let it go ahead so someone can have an empathetic discussion with her about her transphobia over a cup of tea; but as long as they don't lose sight of the big picture, anyone prepared to educate her with kindness has the potential to make a significant impact.
