There is no solution to this problem that doesn't
involve unaccountable third parties setting the
ground rules for what is okay to say
You're confusing this right with Twitter's utterly nonexistent obligation to transmit and amplify your thoughts to others.
I do not think that law is adequate to cover the current state of affairs.
Personally, I'd allow curation/gatekeeping by platforms like Twitter as long as (1) it's transparent (2) there are viable alternatives, including totally unmoderated places where people can post all the coronavirus hoaxes and exhortations to "join the race war" they desire.
It's also worth noting that you are posting this on Hacker News, platform that is far more stringently curated/moderated than Twitter. Why are you here if moderation is so objectionable to you?
You are here presumably because you like the job they do. If that changes you can go someplace else. There are countless alternatives to both HN and Twitter and you can even start your own. Either from scratch, or just spin up a Wordpress site or a Mastodon instance or whatever.
Are you absolutely sure that this statement is correct?
Freedom of speech, as a concept, includes by extension the freedom to be wrong.