I don't see any good middle ground between "authorities can never eavesdrop on inviduals' comms even with a warrant" and "authorities can do mass surveillance". It's a very difficult dilemma. I (as you do) prefer the former if I have to choose. I understand why it's not a very wasy pill to swallow though. Hopefully techniques for targeted eavesdropping (like those you mention) will improve as e2e gets more widespread. The easy of eavesdropping on mobile comms has probably been too comfortable for too long.