The point is, communications should not be surveilled at all by the state. It shouldn't matter that the Internet is sometimes used to commit crimes, the bigger issue is that the vast majority of non-criminal traffic is subject to snooping.
What proof do you have that this is the result of surveillance rather than from responses to complaints?
Were they surveilled? Or simply read on someone's device after they were lawfully arrested, or sent to the police by the victim? You seem to be making a bit of a jump there
Do we know that was the case, for in those instances?
Could be that some guy threatened to kill someone over FB, someone saw that, and reported it.