This group of people have shifted to this position because they no longer have the "de-platform/systemic-censorship" argument that arises when someone is banned from a centralized service, resulting in a total loss of access to the entire platform. Conversely, on the Fediverse they're still there but simply can't talk to some % of users. And that can easily be rectified by being a part of multiple communities and abiding by their rules.
I've tried to write about how ActivityPub (which Mastodon uses) is not a censorship-resistant network and that the point of Federation is to build lots of custom communities and have them politely talk to each other, or ignore the ones that violate community's expectations [0]. Feedback I literally got from here on HN was "I'm disappointed in you", when I think it's an accurate and realistic view. Especially when standing in the shadow of FreeNet.
The same liberty of free-speech and free-association that lets a far-left community thrive, and a far-right community thrive, also lets them block each other (which is a good thing -- it would be ugly otherwise).