If you want something a little more morally clear, take a look at what happens with Sci-Hub. They finally actually lost a court order (which led to the suspending of their hosting), but it doesn't always take that. They've been playing "domain whack-a-mole" for a very long time now: https://torrentfreak.com/sci-hub-battles-pirate-bay-esque-do.... And as that article mentions, less-savory sites such as The Pirate Bay get taken down without court orders all the time.
I also wasn't trying to attack the existing social media sites, either. I think it makes absolute sense for them to kick the trolls and hate crowds off their platform; strong moderation makes for strong communities (HN being one good example).
Mostly, I think I was trying to point out that "go somewhere else" is a solution that only works to a certain extent. Against a relentless enough opposition, there isn't really a true "public square" you can absolutely fall back to on the modern internet. I don't know what the actual argument behind my pointing that out is, just… contributing a fact, I guess.
Gab was banned from the Play Store. If you want to use their mobile app you have to flip extra switches and download it yourself.
Voat was the target of massive DDoS attacks. Also, apparently, people posting child porn there then immediately reporting it to their ISPs to try and get rid of them.
Quillette posted the views of 4 scientists on James Damore's memo and was DDoSd off the net for days.
You have to understand that this isn't a simple case of go get your own infrastructure. The sort of people who want to eliminate "unhealthy speech" on Twitter want to eliminate it everywhere, and will use whatever tools they can get their hands on to do so. Including attacking whatever is set up to support those who are getting booted off other platforms.
But it seems like if that were to actually happen, it would make more sense for pushback to be aimed at those providers, rather than it currently being aimed at private social media companies out of a fear of what providers “may” do if people were to set up their own websites (or use one of the many existing ones).