"just as we constantly debate norms of what speech is socially acceptable, we debate norms about what responses to speech are socially acceptable."
I consider the above section critical in his misunderstanding. The measuring stick by which people are cancelled, here referred to as socially acceptable norms, are in fact not norms at all by any stretch of the imagination. Meaning, these are the enforced norms of loud outrage-addicted unhinged characters forming mobs, not the common norms of the population at large.
Further, there's nothing to debate about these "crazy norms" or their disproportionate responses to non-compliance as they are uncontrollable. Learn how a mob works.
When people cannot express their feelings on political topics, with opinions commonly found acceptable by the public at large, then that is a big problem. It's incredibly dangerous and this is how you get extreme counter movements.
The heart of the matter is not the shouting at each other, that will always happen, it's real world consequences. When they go for your job or inflict life long reputation damage, that makes people anxious to express themselves.
We have to understand that this is a new problem. Before, in the physical world, if you would say something controversial, people might verbally counter you, which is business as usual and the free exchange of ideas, including bad ideas. That's quite a different experience from a pile-on by the mob, smearing you, calling your employer to get you fired, digging into everything you ever posted online to do maximum damage.
That dynamic is new and it has to be fought. It's cruel and sadistic.