Re: A Stalker's Dream
Nice example of how this can spread access to a network without the owner's consent.
If every device used Sense, it wouldn't be as bad an idea. The network owner is the only one who enters the key, it's shared with their friends and no further, everyone's happy. (Of course, as other people have pointed out, this ignores the reality that many people have contact who are not trusted friends.)
If nothing uses Sense, it's possible for friends to pass on wifi keys, but it requires a deliberate action. John could choose to give Mary's key to Charlie, but it's not something that can happen accidentally.
The problem is when you mix key-sharing methods. Maybe Mary uses a Mac and has never heard of Sense. Maybe she uses Windows 10 and turned Sense off because she doesn't want her wifi key shared with everyone she's ever contacted, which includes Charlie. Either way, when John enters the key on his Windows phone, it assumes he owns the network and has the authority to share the key with everyone he knows. Since John isn't tech-savvy, he isn't aware of Sense and hasn't turned it off; he doesn't even know that Charlie now has Mary's key.
The only way I can see this being workable is if it's fully opt-in: choose to share a key, and choose who to share it with, rather than sending it to all of your contacts.