I have mine throttled and they can't access the rest of home network.
Having a guest network also means you are not liable if someone misuses it:
https://www.eff.org/deeplinks/2011/08/open-wifi-and-copyrigh....
https://www.scienceabc.com/innovation/how-can-mobile-phones-...
If that was your sole reason for having it enabled, you can turn it off now.
Public places can easily claim its not them, but for a house I can imagine it can get tricky, specially if its long-term abuse by a neighbor.
Case in point:
https://www.registercitizen.com/news/article/Man-mistakenly-...
The truth was found after all, but the loss of reputation and legal stress are not worth it, specially in your Good Samaritan scenario.
As a side note, I like that almost all new cars will automatically call the police for you when they sense an accident, using built-in cellular systems.
SIM cards should get less relevant over time with e-SIM. Smart watches are leading the way in their adoption.
In many countries the owner of the contract is liable for anything originating from that line.
Wrong. Remember Dmitry Bogatov's case. Yes it was a Tor exit, not an open WiFi, but it doesn't matter. Even worse, there is now a law here in Russia that prohibits running WiFi access points that don't take technical or organizational measures to identify (e.g. get passport or phone number of) the person who is connecting.