"When you open up your trusty laptop, check for available networks, choose one and click 'Connect,' you're instructing your computer hardware and software to communicate with the hardware and software that's providing the Wi-Fi network and ask permission to use the network.
When you do this, a router either grants permission, and assigns an IP address for you to use, or denies permission. If the connection simply works, it means by definition that the network is set up to automatically grant you permission to use it, and to actively provide the means for you to do so. That's what 'connecting to a Wi-Fi network means.' Your computer works on your behalf to ask permission to use the network, and the router works on the behalf of its owner to grant that permission."
Finally someone has the right idea about this.
There is no such thing as "stealing" WiFi, unless cracking is somehow involved. If there's no cracking involved, then it's not even as simple as the "open door of your house/can anyone come in" analogy, it's even simpler -- having unsecured WiFi is the same as having the curtains open on your windows and having someone outside watching your TV.
Are they stealing anything from you? No, nothing that you weren't already broadcasting outside in the first place.