You seem to be overlooking the obvious argument that if a small group of people use encryption, then you greatly reduce the number of messages that you need to flag. Furthermore, if someone on a Watch List starts using encryption then perhaps you have an imminent problem.

I'm not on the side of reading messages but you missed the real argument being made.

Typical HN. How about someone answering the argument that will really be made by governments instead of the pointless one the NSA, etc have already answered. You can downvote me but you don't get a downvote in governments around the world when they outlaw real encryption.