Or you could define an objective standard by which platforms should moderate their content.

I don't think it's possible to define a standard that people with wildly different perceptions of reality can agree is "objective."

If you believe that there is a massive conspiracy that resulted in widespread election fraud, flipping the election results, and that the massive conspiracy is going to ruin everyone's lives in the future, you'll find it objectively truthful to make sure everyone posts as much information about the election being stolen as possible up to and including taking up arms and fighting for your freedom, and there's no way to reasonably interpret that content as harmful to the greater good.

If you believe there was no conspiracy resulting in widespread election fraud, but there is a massive disinformation campaign stemming from a demagogue that now has enough followers willing to take up arms and attempt to overthrow the government, you will find it objectively truthful that posting information about the election being stolen will contribute to inciting those followers and is a grave threat to our model of democracy.

Content is, by its nature, open to interpretation, and often written with persuasive language. If you're persuaded, your beliefs and actions will tend one way, and if you're not, they'll tend another way. The same content can only be evaluated in a subjective manner.

HN posting rules require me to say more than just "LOLOK" so we'll go with this:

That standard doesn't exist and isn't objective. No, even that really clever one you're about to come up with. It's not real. It's all subjective. The entire US legal system is a "Common-law" legal system, meaning it's all subjective. Objective is for mathematics, not the law.

*edited for typo

The quality of laws is also subjective, yet we've somehow managed to come up with working governments that operate somewhere between tyranny and anarchy.

I'd argue that introducing legal uncertainty is part of the goal. When these platforms have to consider that every deleted post could get them sued, they will delete less.