I'm a free speech absolutist, but violent speech, "fighting words," insurrectionist speech, etc. are not protected under any free speech doctrine. Free speech isn't some carte blanche that allows anyone to say anything at any time. That's not how it works†. I've argued in favor of free speech here on HN (and got the downvotes to prove it) more times than I can remember.
But this letter by Gab is absolutely disingenuous. Eric Coomer, a Dominion executive, for example, is not a public person. He has received death threats and is currently in a secure location due to credible threats to his family, children, and parents. At this very moment, on Gab TV, we have a live channel discussing his alleged fixing of votes (featuring Lin Wood). I mean, this is a blatant attack on a private person that has been proven to incite violence.
This has nothing to do with free speech, and Gab is an absolute cesspool of delusional QAnon conspiracies, anti-vaxxers, and adjacent movements. They're going to have a hard time monetizing (just as 4chan did).
† See Mill's Harm Principle.