So, there is an abundance of evidence by now that the more power is held at the top, the more determined ambitious people are to get there. If that means being

So, there is an abundance of evidence by now that the more power is held at the top, the more determined ambitious people are to get there. If that means being the best at manipulating the people and/or computer that is at the center of power, then it is not unlikely that the most ambitious people will succeed at finding a way to do that. Moreover, a single (or multiple) bad government(s) is a big problem, and may take decades for a nation's people to solve, but as long as there are other places (not governed by that government) to go to, expatriates can gather there to discuss what went wrong, what to do instead, and how to bring it about. If a single government dominates all, you are in an it-can-never-fail situation. Or, to put it another way, one world government is the mother of all "Single Point of Failure"s.