Long ago, during the Viet Nam conflict, the US government learned that computers needed to be able to securely process data from multiple levels of classification simultaneously. Research in the 1970s found solutions that were adopted in the Mainframe world, like KeyKOS and EROS. Then the PC revolution swept all that away, and we're here 40+ years later, with operating systems that trust every bit of code the user runs with that user's full authority.

It's nuts. If the timing were slightly different, none of this "Cybersecurity" would even be a thing. We'd just have capabilities based, secure general purpose computation.