"coalesce into slanderous mobs"
Now, of course "the mob" can get things wrong. We see it all the time — and it's not a progressive or "cancel culture" thing specifically. It's just a side effect of these very rapid and short-burst communication platforms that many people use these days. And I'd frankly argue that the fact that bad information is so easy spread has been used to very harmful effect not by progressives but by people like Donald Trump who require these sorts of misinformation campaigns to stay afloat politically.
Maybe you disagree with that last point.
Regardless, if you dislike hate-filled mobs reacting to bad information, then you have to admit that some sort of content control has to be applied by social media platforms themselves. Or else it will continue to happen.
That said, the other part of this is that it's very easy for a large group of people to be informed of and react against something which they perceive to be harmful. Progressives — even cis white male progressives — have every right to be offended and to express their opinions against something they perceive as harmful. I imagine if you're on the receiving end of this then, yeah, it can feel like a coordinated mob and I have no doubt that it can be downright traumatizing. But that doesn't mean it's wrong or that you've been "cancelled." It is, again, a side effect of how our social media is currently designed and I'll be honest that I don't know what the solution is. But high profile writers with huge megaphones need to be aware that people have the ability to read, share, and react to what they write. And even low-level racism, sexism, etc which they maybe could get away with in the past will now be scrutinized. But that's a good thing, because we as a culture need to be scrutinizing how certain beliefs cause people real harm.