The reasoning is simple: if no random third parties ever get full control of your machine, than most likely the OS is going to stay intact (with the exception o

The reasoning is simple: if no random third parties ever get full control of your machine, than most likely the OS is going to stay intact (with the exception of possible local privilege escalation exploits). If the OS is intact, the job of checking whether a user environment is compromised is easy and actually doable (as opposed to the case of trying to find malware on a compromised OS). If, in addition, a user account has limited privileges (which it should of course), then even when compromised the chances of malware being able to do a lot are a lot less. For instance, turning off a webcam light being a root is probably easy, otherwise probably not. Setting up a server, listening for incoming connections and punching a hole in local firewall as root is available, but as a regular user is not. Stop giving admin rights to your computer to random people (install software as an admin) and live much happier. As an additional benefit, there's never a situation 'I installed this and now computer is messed up, because Joe-the-dev ran "rm -f " with a wrong path as a parameter'.