> anyone interacting with the electromagnetic field that you haphazardly allow to escape the privacy of your residence is within their rights to do so

You seem to have an insufficient understanding of how wireless communication protocols work, in particular the 'communication' aspect. Simply detecting the signal would not allow you to use the WiFi network. You would have to establish a connection with the access point and actively and continuously exchange information with it, thereby directly using its resources.

This is not the same as coming across a fallen coin in the street, or reading by ambient light emitted by someone else's candle