No person or organization is really suitable to be the arbiter of truth

Courtrooms are arbiters of truth literally all the time. There are plenty of laws for which truth is a defence, and dishonesty is punished.

When battling misinformation, the problem is not that lying on the internet is legal - it is still actionable. Fraud is still illegal. False or misleading advertisements are still illegal. Defamation is still illegal. Perjury is illegal in the criminal law sense, not just torts. Ask Martha Stewart who the "arbiter of truth" is.

The problem is that it's functionally impossible to enforce on the scale of social media. If 50,000 people call you a pedophile because it became a meme even though it was completely untrue, and this costs you your job and you start getting death threats, what are you going to do about that? Sue them all?

So we throw up our hands and let corporations handle it through abuse policies, because the actual law is unworkable - it's "this is illegal but enforcing it is so impractical that it's legal". Twitter and Facebook don't have to deal with that crap so we let them do a vague implementation of the law but without the whole "due process" thing and all the justice they can mete out is bans.

If you disagree, then I've got a Nigerian prince who'd like to get your banking info, and also you're all cannibals.