Premise: The number of people that a small group of people (terrorists) can potentially kill doubles every X years.

Eventually the total number is larger than a large nation, and eventually the world population. (The population also grows, but they are more concentrated in turn, making them more vulnerable.)

We gotta move on to the stars people. Too many eggs are in one basket.

BTW, any estimates for X? I would say about 5 to 15, and lower if they get nukes.