It appears to me that you misunderstood a term. (Apologies if I’m wrong.) Social justice is a completely different concept than mob justice. To greatly simplify it, social justice is the concept that we should fight to eliminate bigotry.
So they’re not defending mob justice as a whole. They’re saying that, in this particular case, they think that the negative consequences the person is receiving are in fact proportional to their crime. That, because they were so bigoted, the negative speech they are receiving are properly balanced.
I won’t argue either way. But I will say this points out the dichotomy with mob justice. On one hand, it is dangerous. As a whole, it isn’t very discriminating, and can very easily go after the wrong person or balloon into much more than that person deserves.
But, on the other hand, it can be the only way that people face consequences for acts that very much are wrong, like bigotry. Even though such things are just as harmful as many crimes, they can’t be criminalized. The only punishment possible is the approbation of society.
That’s why I don’t talk about “mob justice” as a single thing, but discuss different tactics as right and wrong. I continue to say that voicing your disapproval isn’t wrong. That saying someone should be fired isn’t wrong. That choosing not to do business with someone isn’t wrong. Where it crosses the line is when it become harassment, violent threats, and such.
For example, while your link (in your subsequent post) actually talks about a woman who was harassed, its headliner is a woman who really wasn’t. The only consequences J.K. Rowling faced is of people telling her she’s wrong, not giving her money, and telling others not to do so.
And, given how horrible what she did was–vilifying an innocent minority as some sort of threat to women’s rights–that’s entirely proportional. She’s tried to say she cares about trans people while doing the one thing they asked her not to do–misgendering them, trying to erase their existence. If a trans woman isn’t a woman, then she’s not trans either, and thus she doesn’t exist.
That is hateful, and causes harm to so many. Not only trans people, but those of us who have trans friends. It does harm to any anti-bigotry fight since the argument is classic bigotry: someone is different than you, and you treat them like a threat, even though there are more of you. It’s the same bigotry that was involved in making black people into rapists and thieved, gay people into pedophiles, and women into succubi types.
It’s wrong. It’s hurtful, and it sets back the fight against bigotry which she previously claimed to support. That people don’t want to do business with her, and will tell her directly that she’s wrong–how is that disproportionate to her hatefulness?
Lumping together things like speaking out against things you think are wrong and harassment and death threats under “cancel culture” or “mob justice” often leads to people defending both or decrying both, when they really should be evaluated separately.
Not that even this is perfect. But I think it’s a start. We’ll get nowhere if one side is talking about free speech while the other side is talking about harassment.