Surely this is a relevant distinction?
The other issue is that if the mainstream thing bans certain things, any free speech alternative will be excessively populated by the witches the mainstream platform hunted. This is inevitable especially if the platform is convenient enough to be competitive.
Which is a little tragic since a bunch of the banned people don't get banned just for politically dissenting thought but just plain awful behavior even by other standards. Regardless, it's inevitable, so painting alt platforms as hives of scum and villainy and thus cutting them down being justified more or less ensures that alt platforms won't come to exist in a relevant way.
The fringe spaces will only get less silly if they're allowed to live and we can talk to people. Being able to talk with civilized people doesn't cure political disagreement or argument, but it lets you see the human on the other side of the nickname. I actively hunt interesting people across the political landscape to follow for that reason. Besides, I'm likely to learn something I otherwise wouldn't have from someone reasoned that I disagree with. People with shared politics only go so far. But people also need comfortable base camps from which to explore.