1) Anyone is free to make a Mastodon host with no moderation (except for what's necessary to avoid running foul of the law), but I doubt you'd get a lot of takers, at least not among the sort of people who would build a functional discussion space. Probably you'd just end up with 4chan again.
"You can lead a horse to water, but you can't make him drink": lots of people have decided they want moderation, usually for good reasons involving harassment and abuse. People often want echo chambers too; that's not great for us in the long run, but it's difficult to make a moral argument that people's preferences should be overruled and they should be forced to listen to content they'd rather avoid.
and 2) Mastodon is no worse than the situation now with Twitter: Twitter also has a set of baked-in standards for moderation, and also allows you to live in an echo chamber if you want, with blocking. At least with Mastodon you can choose the type/degree of moderation you prefer.
As it is, the fact that I can see and interact with people on the local and federated timeline (much like one used to in the oldold days of the twitter firehose) means I am in _less_ of an echo chamber than I am on twitter, in every sense.
Your definition of "dissenting opinions" is essential to this. If it's "genuine points of conflicting dialogue", I don't see any squelching of that in the slightest. If it's "hate speech, advocation of violence, etc", then yeah, that stuff has been shut down pretty hard, and I'm happy for it.
This is effectively a repeat of the sub-reddit moderation scheme, but applied to a twitter like messaging platform. Go look around reddit for a general discussion forum where there is healthy tolerant community, outside of very specific limited topics where moderation is focused solely on keeping people on topic you will find moderators who have used their ability to create insulated echo chambers.
Again, I think it's important to be explicit about what you mean by "free and open speech", "dissent", etc.
I don't really see the analogy to sub-reddits, or shared forums in general. On my instance, the only stuff that's eligible for ejection is illegal porn, hate speech, abuse/harassment, etc. If that's an "echo chamber", then we don't have a shared vocabulary here.
""" 'Free speech' means absolutely nothing can be off limits, ever, because in some theoretical future timeline, that means we won't be able to voice controversial opinions. Bluntly, if oven memes are at risk, then that means we won't be able to have dialogue on race relations or tax policy. """
You're right that, in general, this has been the state of affairs on Twitter, and it's a top-3 reason why a lot of people are interested in exiting that platform. Few want to spend time in a 4chan dystopia.
edit: Also this isn't some theoretical, unproven thing that will happen to far future generations. At this point its almost a surety that it will happen in less then ten years.
My goal is to allow as much free conversation as possible on my instance. In general, that means I'm taking a laissez-faire approach to enforcing the rules I've set out (see: https://freeradical.zone/about/more) and not caring unless I have to. But if a user is causing problems, I reserve the right to drop them. If another instance is causing problems for one of my users, I reserve the right to silence or block them that server if that's what's necessary to protect my user.
I have about a million things I'd rather be doing than powertripping on who can post what on my instance. Barring illegal, extremely distasteful, or abusive content, I really don't care what my users send or receive. But I will do what it takes to protect me, my users, and my instance.
On the other hand, I only have to deal with what's legal an acceptable where I live. If an instance in Japan wants to host loli, fine. I can (and have) chosen not to carry their content. If an instance in Idaho wants to host Nazi content, that's up to them; the rest of us can choose not to carry their content.
I won't have to (and can't) come up with global policies.
The first is a consequence of people, the other is a function of Twitter and the fact that you probably read it from a person with lots of followers, who have at least somewhat similar ideas and therefore many are going to disagree with you. Because there are many of them, it can feel overwhelming when they all answer you.
And having not kept my mouth shut during the rocket-guy-shirt fiasco I can tell you that you get the same result when you are on the other side too.
The complaint covers genuine abuse like what happened to Kathy Sierra.
I can only speak to my own observations, which do not support this assertion.
I think people have forgotten the origin of John Gilmore's famous quote, "The Net interprets censorship as damage and routes around it." He wasn't talking about the people of the internet (though I believe he later said it wouldn't be wrong to interpret it that way), but the way the Usenet network would find a way to pass messages across the network, even when some Usenet node operators decided there were messages they didn't want to pass.
Those who do not learn their history...