They are illegal, yes. But when they're done anonymously, it's rather hard to investigate. And apparently, people seem to think it's just fine, because hey - some of those people came out of it just fine, no big deal!
You know that if there's an investigation, a warrant can be issued to get all information from Twitter, Google, Apple, whatever, right? Just like the rest of your narrative, it just relies on distorting what reality actually is.
But more importantly: your argument seems to be, or at least imply, that if some action X (e.g., protesting someone) MIGHT SOMETIMES be done in conjunction with criminal activities Y and Z (e.g., libel, sending death threats, etc), then somehow that means X is inherently horrible too.
Which is textbook association fallacy:
P1: A is a B
P2: A is a C
therefore
C: All B are C
In this case:
P1: X is (an example of) a cancel culture tweet
P2: X is also horribly morally wrong (on account of being a death threat)
therefore:
C: cancel culture tweets are horribly morally wrong
But there's a reason it's a fallacy. It's broken logic.
By literally the same logic:
P1: The protest in city X was a BLM protest
P2: The protest in city X was morally wrong (because it turned into a violent riot)
therefore
C: BLM protests are morally wrong
That's literally the kind of nonsense guilt by association that you keep peddling.
Here's an idea: if you have a problem with death threats or libel, then just speak against those. I wouldn't even mind more people speaking against death threats.
But damning something by association is just utter nonsense.