I'm surprised that this basic foundation of the popularity of "cancel culture" doesn't get pointed out more. It's dead obvious, and something virtually everybody can sympathize with, whether they admit it or not - but people want to find other, more easily attackable qualities to describe cancel culture as being "about". Like most topics that consist mostly of irrational side-taking, it would be a lot less messy to just criticize specific examples, instead of making it into culture war on purpose by forcing it into the mold of the monolithic "them" vs the monolithic "us".
>against just about anyone all the time
These are exaggerations. It sounds like you're harboring an irrational hatred for "SJWs", and are using misdeeds conceivably attributable to that group, however you define it, to rationalize the delegitimisation of anybody who seeks to expose harmful behavior.
I'm sure that's related to the definition of cancel culture in some contexts, but none of the people signing or intended to be swayed by this letter sell any products. This letter is specifically talking about academic bullying as a means of intellectual suppression. That has little if anything to do with products like Facebook, I really don't see the connection.
I’d argue that’s not the point of cancel culture. I think cancel culture is the result of unethical actors not getting punished by the people in charge any more. The only way you can punish them is to not buy their products.