" And you want to intercede on an arbitrary method you just made up,"

No, they literally identified a plausibly sensible policy flag, not some arbitrary action.

These flags are used in literally every system imaginable.

They they don't conform to some hard criteria, to your criteria, or to some working or ideological group's criteria is a bit besides the point.

Every system has these for good reason.

We have laws and regulations for all sorts of things to help people - including children and parents - in a complex society.

"The state has no business listening in on private citizen's communication."

The absolutely do, depending on circumstances. While Facebook is not a place for state monitoring, it's definitely in the public interest if they flag something that is 'very bad' by some reasonable criteria, so that the state can then act if necessary. They do so within the boundaries of the law subject to judicial oversight.

Facebook is a popular social network, a place that they want people to feel imminently safe. It's a Starbucks lounge without coffee - not a 'personal hyper protected zone'.

Other places, such as Signal, Telegram etc. can have different levels of privacy aka e2e given the different offering and expectations of privacy.

Facebook more or less wants to offer a relatively safe place where the kids can hang out, where they know crazy people are not going to attack their kinds. It's a community centre not a hacker zone.

If we can get past that, then we can move onto basic issues of privacy, advertising etc. which are damaging to everyone, especially young people, for which Facebook has perverse incentives.

"The state has no business listening in on private citizen's communication."

The absolutely do, depending on circumstances.

So primary is this concept of privacy, that it requires an entire legal framework, evidence of potential wrongdoing, proof that there is no other method to achieve the goal of validating guilt, proof that the crime is severe, and not a hunting expedition, approval via a warrant after a judge has examined that evidence, and strict controls around the entire usage of that warrant.

Wikipedia says:

Lawful interception is officially strictly controlled in many countries to safeguard privacy; this is the case in all liberal democracies.

Using this edge case as "depending on circumstances" is clearly not the generic I was referencing. The statement that

"The state has no business listening in on private citizen's communication."

Is valid, correct, accurate. Listing edge cases, is not invaliding the rule. It is the exception to the rule, and considering the sheer volume of communication, compared to the volume actively tapped in a legal means, it is the most edge case of edge cases.

There is no reason I would deem a mega-corp to somehow be OK to do what I would demand the state not. That our democratic societies have deemed that our states should not.

To highlight that, the phone companies of old would be in infinitely hot water, should they listen to communication between customers, in any fashion.

A platform is not a parent, should not police, should not act as an arm of the state, or as an arm of parents, except as I stipulated, by direct request of the parents, and only to enable the parents to be a guardian. Under no circumstances should that involve the platform scanning anything, instead, the platform could simply give parents direct access to a child's account.