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.