They want freedom from the consequences of their shitty speech

Sartre said it...

Never believe that anti-Semites are completely unaware of the absurdity of their replies. They know that their remarks are frivolous, open to challenge. But they are amusing themselves, for it is their adversary who is obliged to use words responsibly, since he believes in words. The anti-Semites have the right to play. They even like to play with discourse for, by giving ridiculous reasons, they discredit the seriousness of their interlocutors. They delight in acting in bad faith, since they seek not to persuade by sound argument but to intimidate and disconcert. If you press them too closely, they will abruptly fall silent, loftily indicating by some phrase that the time for argument is past.

Because they don't understand what freedom of speech means, plain and simple.

I don't disagree with your premise, but what if they are doing the bidding of the government? Would you consider that being a defacto arm of the government? It's currently being played out in the courts right now with the latest move was a judge put in an injunction barring the white house from communicating with social media companies.

If there is one good thing from Elon buying Twitter it's him releasing the Twitter files showing that social media was doing things at the behest of the government in the aims to censor people.

What other established constitutional rights would you support large institutions not respecting as long as they aren't directly run by the state?

We're literally talking about Meta here. The claim that their actions are those of an independent private company are about as credible as if Lockheed Martin were forcibly quartering soldiers (err... private military contractors) in people's homes and claiming that wasn't a violation of the 3rd amendment.

Not a fan of that argument. Twitter/Threads/Facebook/Reddit/etc are big enough to be considered a public forum, even if they're being controlled by a private entity rather than a government.

Ironically, it does apply to corporations - just not in the way that you think.

Corporations have the right to freedom of speech - meaning they can choose to allow whatever the speech they like. Consequently, they can also choose to disallow whatever speech they don't like.