But people can also choose their instance, and there are enough instances out there that it's hard to force all of them to defederate.

I use lemmy.today as my home instance. They explicitly state in their instance policies that they want to avoid defederating with instances if possible, and so far, have no defederations. As long as there are instances like that out there, you cannot really muzzle someone.

Avoiding censorship doesn't mean that people are required to consume content, just that they have the option to do so.

There are two major risks that I think do apply (though the Threadiverse is no more vulnerable to either than Reddit):

• State censorship. Countries willing to, at the network level, ban instances or instances that federate with instances (and possibly also VPNs, though even without that, the bar to see a post is increased) can make it hard to see content. This happens, at least in part, today. One of the first discussions I was in was one where Ada, the instance admin on lemmy.blahaj.zone (transexual-oriented instance), was talking to some guy in a majority-Islamic, Middle Eastern country whose government had blocked access to lemmy.blahaj.zone at the network level. He could see posts by using a federated instance that they hadn't blocked, but not images, since those were served directly from lemmy.blahaj.zone.

  Right now, the Threadiverse is still small enough that it'll fly under the radar of some governments. But as it grows and becomes more prominent, media becomes of more political interest to governments.

• The potential for a Thresdiverse Cabal. It is possible for enough instance admins, banding together, to potentially form a cabal and to have significant influence over the system. In the past, this sort of thing has arisen on federated systems:

  https://en.wikipedia.org/wiki/There_Is_No_Cabal

  There Is No Cabal (abbreviated TINC[1]) is a catchphrase and running joke found on Usenet.[2] The journalist Wendy M. Grossman writes that its appearance on the alt.usenet.cabal FAQ reflects conspiracy accusations as old as the Internet itself.[3] The anthropologist Gabriella Coleman writes that the joke reveals "discomfort over the potential for corruption by meritocratic leaders".[2]

  The phrase There Is No Cabal was developed to deny the existence of the backbone cabal, which members of the cabal denied. The cabal consisted of operators of major news server newsgroups, allowing them to wield greater control over Usenet.[4]

  That being said, even the Usenet backbone cabal had limited control, and the Fediverse's protocols are probably more-resistant. Usenet's NNTP relied upon traffic flooding through the network over a set of fixed links. Esch NNTP server has at least one other NNTP server that they are connected to. That upstream server could block content or filter posts, and downstream wouldn't see it. ActivityPub has every instance (potentially) talk to every other instance. I'm not sure that that won't lead to scalability issues in the long term, but it also makes it hard for operators of major instances to control what other instances see.