Once I got doxxed by bloggers from one end of the political spectrum who thought I was a blogger from the opposite end. (We have similar names, but the doxxers put out all of my info. I generally try to avoid making extreme political statements publicly on the internet.) Even after I got my info taken down, someone archived it and the archives got passed around on Twitter, prolonging the mess. Even now all that stuff shows up if you google my name (which I could see being an issue in employment and housing searches, for instance).
I'm not asking anyone to care about what happened to me, I just want people to think about the consequences of a system that can't be moderated. If some bad actors can continuously re-inject false information about normal people into the internet, it can have negative effects on the lives of those individuals. Advocate for an uncensorable internet all you want, but you should also be honest about the potential ramifications.
And it's probably better for society in general that communities work that way. You don't want millionaires and oorporations controlling discourse, and in many cases, there are groups and communities who simply physically cannot use the same platform (those on complete opposite sides of the political spectrum for example).
I was on an emulation forum for several years in the early 2000s that had people from every walk of life, every stripe of politics, on essentially every continent of the planet, yet the number of regular users was still within Dunbar's number, for years. That's not going to happen nowadays. If you can reasonably attract ten users, you can and probably will attract several hundred, or more, in much smaller timelines.
This is borne out by looking at Mastodon instances right now--there are ~200 out of ~3000 that fall within reasonable estimates of Dunbar's number and there's no guarantee that any of them will be stable even in the short term. It's a Great Filter for comprehensible human communities.
Secondly, the notion that by federating or centralizing, you can avoid or generate discursal control is pretty unfounded. The 2016 US Presidential election and Brexit are more than enough evidence of that. People can and will use any capacity within their reach to influence discourse, regardless of who owns or doesn't own the infrastructure.
I'd argue that federating generally allows for more pernicious discursal control by monied and corporate interests, solely through the lack of singular points of control. If you can automate contact and distribution, which is already trivial, you can spread whatever you want as far as you please as much as you like, knowing that if 90% of administrators remove it, you still have 90% possible impressions and 10% of instances that haven't removed it. If the content is even remotely infectious, it'll immediately spread back to the 90% by the 10% of users, anyway. Chain-letters are great examples of this in action (and in their more modern forms "upvote this if," "retweet this if," and "like this if").
Control isn't binary. Facebook can exert much control over discourse while still being vulnerable to powerful actors.
The idea that I'm primarily disagreeing with is that Facebook, Twitter, et al. can be hegemonic in a user-populated space. I don't think they can. They can certainly exert large amounts of influence and constrain it, but it's not monolithic and they don't control it. Federation only makes that influence more invisible. It certainly doesn't remove it.
Just because not all problems can be solved with Mastodon, and the like, does not mean they are not worth pursuing.
Are humans in large numbers capable of interfacing with individual human beings without engaging in pernicious behavior? The answer, as anyone online in the last twenty-five years is a resounding no. Are humans in large numbers capable of behaving immaculately when it comes to preserving their own or their customer's privacy? Once again the answer, as anyone online in the last twenty-five years (and several decades longer if you include proto-business networks) is a resounding no. If you add progressively more humans to anything, does the output improve? If the metric is human satisfaction, the answer is no. If the metric is the rate of return in a Ponzi scheme, then yes, okay, you've got me there. The cause of almost all problems is solutions.
As far as social media goes, it's literally designed to use people to promulgate human-motivated pseudo-information for as long as humanly possible. It's not for "socializing" or "meeting people" in the same way that TV shows and movies aren't there for entertainment. It's to sell the viewer's attention to people that have anything but their interest in mind. Moving to federated enclaves is just further deregulating an already throughly pernicious industry.
Self hosting a service will of course mitigate all of the issues you listed. The control shifts from a company like Facebook into the hands of the server owner.
Of course, the forces are now politically/socially based rather than fundamentally racially based, but the principle remains the same. It's another digital White Flight by any other name.^1
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1 https://www.technologyreview.com/s/419843/did-whites-flee-th...
People think it'll resolve or at least mitigate the issues of digital privacy, digital harassment, and digital overpopulation, but in reality will just create ever more wasteful and unaccountable digital sprawl while inevitably recreating the exact same problems (e.g. HOA discrimination, nosey neighbors, hiding all non-conforming traits lest your cohabitants judge you, etc).