They don't need their bandwidth!
Does that make it okay for me to jump onto a half-empty subway without paying? They don't need the extra space.
Your rights end when you start broadcasting onto my property.
If you blast your stereo all night and it is annoyingly audible from my property I should have the right to call the police.
If you blast free Wi-Fi and it is publically available from my property I should have the right to use it.
If you throw bags of money over the side of my fence I should have the right to keep it.
What if it's encrypted?
If it's encrypted or password protected then it's common courtesy not to try to circumvent that.
But if it's unprotected then the default position I must take is that they want their family, friends, and neighbors to be able to use it undisturbed.
The same goes for visual photons; if you don't want the whole world seeing your personal business in your room keep your shades closed. If you don't mind people seeing what goes on inside your room then keep them open. You can't tell me not to look at your house.
Once you start broadcasting sounds, light, images, or signals onto other people's property you can't demand that your neighbors shut their eyes or not access it. You don't have an expectation of privacy when you're trespassing your publicly accessible signals onto the property of others.