If I request permission from you and you agree, and I come inside to watch a game on a cable channel that I don't subscribe to at my house -- is that stealing?
It's impossible for me to connect to your wi-fi without your wi-fi giving my computer permission to do so.
Youre missing the point... An unlocked door does not grant explicit permission to come into my home and plug into my network. An unlocked connection (as dumb as that may be) also does not grant you explicit permission to use my network.