The only part of my computer I care about are my own files and of course things like passwords in the Secure Enclave. If the operating system gets hosed (see the former Chrome bug where if you turned System Integrity Protection off and installed Chrome it hosed your entire OS), that’s an annoyance. But recoverable.

It’s actually the concept of an old XKCD

https://xkcd.com/1200/

It sounds like you're treating "a shared folder" as a synonym to "all user files"? Those aren't the same thing? E.g., a shared folder can be a far smaller subset of all a user's files?

(Also, Apple's sandboxing supports access to a single files, reference https://developer.apple.com/documentation/security/accessing... so not sure if any of this is important anyway.)