The author seems to mistakenly believe that Linux is a multi-user system where not everyone has root privileges. The reality is that almost nobody uses it that

The author seems to mistakenly believe that Linux is a multi-user system where not everyone has root privileges. The reality is that almost nobody uses it that way, it's not tested for that and due to the huge API surface area the chance of some kind of exploit is so large that it cannot be secured even if it people tried. The only reason "root" exists currently is to make it less likely to accidentally change or destroy the operating system. There is no way to provide a multi-user experience on a physically accessible system (cannot defend against physical attacks), and the way to provide it on a remotely accessible system is to assign a virtual machine to each user.