I feel like you're talking about two different types of people. Let's face it: people throw around -phobes and -ists way WAY too easily. Many times, the person on the receiving end would never consider themselves to be whatever the label thrown at them is. IIRC, Rowling does not consider herself to be transphobic or a TERF so when she gets approached in that way, it really doesn't do much to help. Those types of people I do believe you can talk with and at least come to an understanding. If she says something factually wrong, the best thing you can do is use your voice and own platform to spread the correct information. But screaming out -phobe or -ist, people are just going to shut you out and ignore you (general "you" here, don't mean anyone specifically).
Then there are the people who are actually part of brainwashing groups who are really just looking for a place to belong or let out their rage at the world or whatever. Those people need help in a completely different way. No matter what you say to them, it doesn't matter. I watch a lot of flat Earth "debates" and I can tell you, a lot of them repeat the same things over and over. This is because flat Earth is basically like a cult and they spread around videos and have discords/FB groups where they repeat the same thing. No matter how much evidence is presented to them, they absolutely refuse to see it. Presenting arguments doesn't help and many of them need real, professional help and someone close to actually get them out of the group.
Onto the issue of the thread, I'll just say that I agree that cancel culture is complete BS. It doesn't do anything, it oftentimes backfires and it only riles up people and pisses them off and divides us more. If you don't like what someone has to say, use your own platform to say what you think is right. At the end of the day, we will never agree with each other. We will never completely understand each other. Oftentimes, the intentions of the person saying or doing the thing is misunderstood, especially on Twitter with its character limit really, really doesn't help.
The only time cancel culture works is when someone has gone out and committed an egregious crime. Like I think most people can agree that Shueisha continuing their contract with the Rurouni Kenshin author is wrong, though thankfully they did cancel their contract with the writer for Act-Age who had gone out and attacked two middle school girls.