I think it's become abundantly clear that absolute free speech is not an unalloyed good for anyone, especially when confounded by the profit motives of massive corporations.

Not at all. I think it's become clear that all the attempted solutions to the 'problem' of free speech have worse consequences than the problematic speech itself.

And your solution is to have the government be the absolute arbitrator of GoodThink?

I, for one, am absolutely willing to die on that hill.

I mean we've had two decades or so of unelected unaccountable businesses doing a half-assed job of it, and the results speak for themselves: radicalizing pipelines, thought-bubbles, violent and disturbing content, up to and including CSAM, harassment campaigns, people being bullied to sewer-slide, alternative (or no) medicine groups getting people killed, horse de-wormer, do I need to keep going?

And it's not as though truly systemic subversive thought thrives on the platforms either, they're reliant on the government's approval same as anybody the fuck else to continue operating so it isn't like Big Brother doesn't already have his fucking hands on the wheel anyway.

Like at this point, "big government no like" is just not sufficient anymore. The Government already censors shit it doesn't approve of. Your dystopia is already here. You're sitting here complaining about the potential fire of an unattended candle in a house that already has a bonfire set in the living room. You aren't wrong but we have much bigger problems to address.

If you have a solution that doesn't take away rights from large portions of the population whose only "crime"[0] is they hold opinions you don't agree with then I'm all ears.

The person I saw the other day with a "Fuck Biden" sticker on their jacked-up pickup truck has exactly the same right to express their opinion as someone who thinks them driving around in a gas-guzzling monstrosity is a crime against humanity. Now, if either one of them tried to impose their will on the other by, say, destroying the truck or, umm, attempting to sodomize the president then the government has the right/obligation to intervene but before then they should be absolutely powerless.

[0] obviously not talking about things like CSAM which is an actual crime

Your entire argument here is basing that people have a right to express an opinion on a social media site which is categorically false. They have the right to express an opinion, sure, as does the guy with the sticker. He does not have a right to a digital megaphone with which to do that: that is granted to him by a platform like Facebook.

Nah, my argument is based on:

"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances."

Nowhere is mention of 'amplitude' of speech.

If Facebook et al want to restrict what their users say then good on them, they are a private entity and can do whatever they want. Destroying these platforms because they allow speech you don't agree with is not the job of government.