How do you define actual connection to the network in case of WiFi ? Why connecting vs "sniffing" would make a difference as far as privacy goes ? I don't understand why you make a difference between opening a letter and sniffing wifi network communication on an "ethical" POV.

I think it is reasonable to expect the same kind of privacy independently of the technical means for the communication channels between well intentioned people. Of course, you need encryption because people are not well intentioned, but not using it does not justify the wrong behavior.