First, I want sources. Second, these aren't FBI investogators looking, so it's not the same thing.
Another flaw in your reasoning is the human versus machine difference.
LOL
Once you let machines read or record data traffic, the genie is out of the bottle. An analogy to what you are claiming would be letting a machine tape record a phone conversation be legal so long as no person was allowed to listen to the tape.
No, your argument is like saying that since the phone wires "listen" to conversations, humans in general and federal investigators in particular can too.
With sniffers on the internet, you've got a broad spectrum of people including technical personnel who just happen to be FBI, as well as techies in every other company, all watching the plain text data traffic for diagnostic purposes as it crosses problem areas of their equipment.
Why would you call viewing plain text data packets different for one group or another?