That's not the problem - choosing to give up your own secrets is fine, but giving up the wifi password of your friend's router because they kindly let you use the network whilst visiting is not cool at all. I personally refuse to allow access by friends with Android devices, and they are shocked to learn what Google does when I explain why...
At home, and everywhere I've had a say on how the network is laid out during working hours, I treat wifi as external. They get internet access, and there's a password to prevent the neighbours kids downloading GBs of pr0n, access to internal resources require connection over the vpn.
This has the side benefit that all my devices can connect securely to home resources wherever I am in the world.
