…and help the customer reconnect all devices on the WiFi?
If a password is so precious that you share it plaintext with third parties it is a bad usecase for a password.
Treating the network as untrusted is good but as long as some people are paying for service, traffic and bandwidth there are reasons to not allow anything to use your network. And there is also a legal question of liability if someone is not quite above board from your IP.
I've had calls lasting over an hour helping customers configure their email on their phone and computer.
I learned not to laugh when people called "the internet" either "that e-thingy", "mozarella foxfire" or "googlé charome".
I dealt with explaining to people why IE6 did not understand SNI when we decided to give all our customers websites HTTPS.
Just saying that I've been in that and seen that.