When you talk with someone over the phone, perhaps it's strange to guess that there is a "man in the middle" listening. Hackers refer with this terminology to those attacks where at least a channel has an interception point between two sides, and it looks that billions of calls are being recorded each day with an alike procedure.
In the contract of the service, usually there's no information about this channel feature. Business calls, family, sport, intimate relationships with doctors or other professionals; in the end any aspect starts to be considered public at a degree. However, multiple of these communications come from private scenarios, even at home, and this place is right now protected by different constitutions around the world because it's considered a basic right: the right to privacy in your own home, or what you say on it. Some areas severely punish who intercept private communications, although if who establishes the punishment does it, it is strange at least.
If you install a camera as a third eye between the people's eyes, and record every visual perception and sound, there's also quantitative data for national security or other kind of protection to a country. Of course there are who use the phone for talking about crimes and being warned helps save lives or other forms of damage, but it seems a bit ingenuous to think that everyone uses the same channel or say cryptographic algorithms so it would use these channels without considering all what's online about data acquisition systems in telephone, or other hardware and Internet.
If there's a recording, it must be handled by a group of professionals as well. And here, in any moment, you could guess that it could lead to security leaks, misuse and corruption. Pretty popular those movies where there are systems with the ability to have "an enormous power" to be listening from whatever place and have information of whoever individual. A plethora of fantasy that technology is starting to permit at a considerable extent.
Back doors, underlining processes, even if you think that the device is manually stopped, it could be programmed to reactivate itself and record or send data. Nevertheless, today a user with a bit of knowledge about the involved technology would identify those packets being released from any source. In the same line, as it was mentioned, creating unique algorithms to obfuscate the communication. This is another kind of power in the public domain and so, any argument about the necessity of these tracking systems for security has and maybe doesn't have background in a higher percentage. Is perhaps security not the only reason? The curious aspect today is that secrecy cannot be guaranteed 100% and each day a new light could unmask a very outrageous setup of activities (another time) so we think the better policy is to never stay on a side where a focal point makes scandalous headlines around the world, with faces and names.