If you set up your network using radius, this becomes a non-issue radius is not horribly hard to set up either - its also not automatic, the user has to choose to share the wifi password - which they could do anyhow, as you've given it to them to connect.
https://www.windowsphone.com/en-gb/how-to/wp8/connectivity/w... - Section: "I'm concerned about sharing WiFi networks. Can you tell me a little more?"