I love this post, but in current depressing times it need an *.
We let got of real people, and things that do real life harm. That's the things that matter. We don't care for meaningless stuff that doesn't harm anybody.
We stop buying books, and watching TV shows, and going to convention meet-ups, and talking about celebrities when they do bad things. Those things actively give them money, and make the companies keep working with them which pays them and keeps them relevant.
We don't harass people online because they keep doing fandom shit. That doesn't matter. Will Byers doesn't support Israel, Harry Potter isn't funding transphobic laws. Mera doesn't abuse Aquaman. They're fictional and if they bring someone fun to play in their Barbie house, that's fine.
If nothing else, critical people keeping active in fandom means that new people have critical voices around to make them aware of the problems when they join, instead of positive echo-chamber. So they have higher chance to also chose not to give real people doing real harm the money.
Activism has merit when it's worthwhile - and nobody will cancel giant franchises out of existence. You can't silent treatment a theme park and 15 blind box series out of existence under capitalism. What you can do it stop spending money when specific people are involved, so the companies stop working with the specific people. That's the only thing that works.