For added context, here's the archived letter (hosted by Harper's) being referenced by Shadi Hamid (a Brookings Institute fellow and "Senior Contributor" to The Atlantic).

In addition to said letter having signatories that's all over the place politically (including Atwood, Chomsky and Cathy Young in the same list), Hamid continues:

This has been the golden age of furtive text messages and private group chats. Over the past month, I've gotten hundreds of messages from people (PoC and white alike) about how they're quite consciously suppressing their opinions and ideas in public

If you're unimpeachably woke, then by definition you won't see "cancel culture" as a big deal, because, in this particular instance, you're on the right side of cultural power. As my woke friends will often point out, this has always at least partly been about power

Of course, the catch is that no one is—or can be—unimpeachably woke. The creed is always changing and "progressing," so by definition it needs to eat its own at regular intervals. That's also how you maintain and enforce in-group solidarity

It's the less financially and professionally secure who will be affected most by this chill on speech. If you're a young, aspiring journalist or academic, you—especially if you're white—have no incentive to say things that would've been considered normal and boring two years ago

I suspect that this is precisely the point though: From a wokeist perspective, the chill on speech isn't a bug but a feature

From what I could glean, Hamid himself (along with Harper's) has been targeted by those same mobs, and has realized that those pushing "cancel culture" or "woke" BS are a threat to themselves and everyone else.

At minimum, it's a very clear case of self-awareness, especially among those from the Leftist intelligentsia, that they too would pay the price for "woke" BS, and that stifling free speech would also backfire on them.

EDIT: Polishing