While this is obviously a concern you should take into consideration, I believe it can be assuaged by carefully limiting the scope of what this event triggers. Obviously having an arbitrary guest present should never disarm security. My intention would only be to automatically transition from Home to Guest mode, wherein lighting automations are modified.
Someone that needs temporary unaccompanied access should have something like a dedicated keypad entry, but this seems like a good way to keep my motion-lights from turning off when I’m sitting by the fireplace in the living room with guests.
Here’s a similar script that could be modified for this purpose fr dd-wrt; it should be fairly easy to change it from checking for known MACs to checking for anything but known MACs.
https://community.smartthings.com/t/presence-detection-using-dd-wrt-router-script/13731