"Whatever the arguments around each particular incident" carries a lot of freight here. If the signatories don't agree about the specific cases under consideration, how can they make a shared general argument? https://harpers.org/a-letter-on-justice-and-open-debate/
If you're going to make a general case for the illiberalism of a huge swath of society, you have to build that argument on specific examples. To do otherwise is, dare I say it, illiberal.
Because the claim you're making depends—has to depend—on the particulars of the ills you're describing.
Is it bad for a "book [to be] withdrawn for alleged inauthenticity"? Well, that depends on the book, and the inauthenticity, and the process that led to the withdrawal. It has to.
And it depends, crucially, on the perspective of the observer, and the principles they're bringing to bear.
But of course it's far easier to make the general argument, particularly if you're afraid that people will be angry about what you have to say about a particular case.
And yet the distinction between "I don't like it when people get angry about what other people say" and "I don't like it when people who are angry about what other people say do X" is the essential one here.
Nobody has a right to say stuff that other people find obnoxious without getting dragged. When someone gets dragged, the civil libertarian remedy is clear: The cure for bad speech is more speech. Period.
But the letter blurs this line, complaining at one point about "an intolerance of opposing views, a vogue for public shaming and ostracism," and at another about people "who fear for their livelihoods if they depart from the consensus." These are not the same thing.
People I respect signed this letter, and I suspect that if we sat down to discuss particulars, we'd find areas of agreement. But I'd far rather have seen the arguments the signatories had "around each particular incident" than this attempt to paper those differences over.
Because no document that consigns its support for "robust and even caustic counter-speech from all quarters" to a "to be sure" clause can ever really serve to advance such speech. In my opinion.
(Oh, and as this brilliant piece from @OsitaNwanevu makes plain, civil libertarianism that doesn't grapple with principles of associative freedom—particularly in our present moment—is sterile and useless.) https://newrepublic.com/article/158346/willful-blindness-reactionary-liberalism