> Just because it requires a trivial bit of technology to 'listen' to a radio broadcast doesn't make it any different than blasting sound or light waves
In many cases it would be illegal to use a fancy (or not fancy) microphone to listen to your neighbours through a wall, and why should it not be?
It's one thing to accidentally overhear something, and another to deliberately go out of your way to spy on others. Even most(?) US states have wiretapping laws which prohibit such activities.