I for one don't think that this will ever work for the simple fact the humans crave power. Think of it this way. Fidel Castro started out for very good reasons but he became power hungry and turned his land into a dictatorship. Now no government is perfect so how is one government going to run the whole world. This would also cause multiple acts of terrorism everyday because you know some people will plot together and try (or will) overthrow the government. This would also cause numerouse revolutions and many wars. Now you might say that there would be no countries to fight but large groups of people will band together and revolt, thus causing more problems. This idea sounds good in theory but will never work under real circumstances.