Originally Posted by Mrs Beanbag
that's a good example of the idea, but this on its own won't give you any useful protection. It would prevent you from little accidents, perhaps, but...
1. it prevents ALL users equally, so it would also prevent legitimate filesystem writes to protected files, by processes that you might want to have privileged access.
Protect already has a USER flag for that purpose, but mainstream filesystems don't support it. I think it came into being as part of Envoy.
I still don't see much point in multiple users for the sake of security. Sure, it's useful for other purposes such as sharing your computer with other users, but as long as you're the single human user, there's no intrinsic need just to keep up security.
I use my Mac as a single user. In case I need to alter a protected file, the system asks for my password. It could just as well ask for a password without being multi-user.