Wouldn't the analog counterpart be the postal system? They have no right to poke in your private communications.

Edit: That said postal systems are generally owned by the government. So I suppose ultimately (if nothing else) it would be up to their T&C. But I don't see how they could reasonably justify monitoring the traffic. It's not like it's a PR issue for them what users share through their tubes. I would imagine it'd make sense to have them regulated similarly as the postal system (ensuring private communications).