Freedom of speech, as a concept, includes by extension the freedom to be wrong.
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?
The (hopelessly naive) ideal many of us had was that, by breaking down communication barriers, we'd create an egalitarian "marketplace of ideas" and the best ideas would win. And by "best" ideas we generally meant principles of equality, science, and so forth.
Regardless of what you feel needs to be done... I'm sure you can agree that hasn't been achieved. Probably more like the opposite.
The problem is that by amplifying all voices, we've simply created another "might makes right" situation. Unfettered online discourse is dominated by those who yell the loudest. This includes a large number of woefully misinformed people, and genuinely malicious actors such as (for example) the hordes of paid internet trolls funded by America's rivals in order to sow discord and disinformation during our 2016 elections.
In effect, we've replaced the staid and conservative corporate self-censorship of decades past with something that is quite frequently worse.
I mean, free speech sure sounds good, but in reality it means that your racist uncle ranting about chemtrails on Facebook gets to be heard right alongside people who actually know what the fuck they're talking about.
I unapologetically do not know what the solution is.