© Charles Chandler
Operating systems are way too vulnerable, to user error, to malicious software, and to errors on the part of the application developers. It's possible for users, malware, and poorly-coded software to make system and application changes that result in the breakdown of some or all of the functionality of the computer.
These errors are encouraged by the fact that all of these system and application files are exposed to the user, via the operating system's file management interface (i.e., Explorer or Finder). When opening, saving, renaming, and moving files, the user is constantly exposed to files of which he/she has no knowledge. This is as inconvenient as it is hazardous.
Attempts to solve the problem with user rights of varying degrees have only succeeded in inconveniencing the users as well as the developers. After the 11,000th time that a user has to click the "continue" button in a security alert dialog box, or type "sudo" in a terminal window, it becomes something that the user just doesn't think about.