My home wifi is, and always will be, unlocked and open for anyone to use.
Why? Because sometimes when I travel - or sometimes if my home network is down, I need to borrow from others. Also, sometimes I enjoy hearing from friends when they travel, or their home networks are down.
And sometimes others might need to borrow from me.
Some would call it theft. The borrower is using something they didn't pay for, and if they want to use it they should pay for it themselves. But wifi isn't a zero-sum commodity. That someone else borrows mine takes nothing away from me. I still have the same service and pay the same monthly fee. I prefer to call it sharing.