Niven’s Law says that if it is physically possible to build time machines and change the past using them, then a stable world is one, in which no time machine has ever been built and operated. This is so because if some inventor built a time machine at a certain time, then in the future, there will always be a time traveler, who changes history so as to prevent the builder from building his time machine.
This assumes that a single brilliant inventor invents a time machine. A single person can be blocked. This is a single point of failure.
However, what if the world has technologically advanced to such a state that there are millions of people, who have the know-how and materials, so it takes only a small leap for them to build a time machine?
My thesis is that such a case represents a loophole in Niven’s Law.
This is so because it is as possible to block development of a time machine as preventing superheated water from eventually boiling, or supersaturated salt solution from eventually crystallizing all excess salt. Water needs to be cooled or the salt solution needs to be diluted. In the case of human technology, this means setting the technology back – shutting down the Internet, having a large natural disaster, etc.
Otherwise, no single time traveler from the future will be able to block all people, who are capable of building time machines. There would be no single point of failure, such that acting on it would prevent the world from having a time machine altogether.