Mastodon instances are all private property. They are clubs that can be run according to the wishes of the owners.
> You can't prosecute us for things that are published as we are a platform for communication, we're not responsible for what's communicated!
> We can moderate and ban you for saying things we disagree with based on what we interpret our "rules" to be (in social media's case: whatever the West-Coast likes and Copyright violations)
With Mastodon (or phpbb forums of yore) the former is false, so it's at least internally consistent, and of course you have the choice to move away, it's not 1 moderation style for the whole planet across all cultures.
We have that, with public roads and parks.
"Here's the rules: don't litter, don't get naked, don't yell and follow people"
What I'm saying is that you can be one or the other, but not both.
Mastodon doesn't pretend to be anything other than private property.
Twitter pretends to be a public place, like a park or a giant square.
small private forums also had some draconian moderation (well, some of them did for sure), but the key point was that they were small, targeted and competitive with each other.
Too draconian, and people leave; too loose and people abuse.
The thing is, you kinda know what you're in for with small forums (or in this case mastadon instances), the servers themselves do more to say what they're targeting and what niche they have; they do not pretend to be an apolitical platform or to not have opinions.
That's the major difference, you can go to other Mastadon instances and find people you enjoy being around. With Twitter there are some hidden "rules" (which used to align with the US west coast ideals, and now seem to align more with the trumpy right-wing thing), with Mastadon it's more likely that you know what the rules are.