[Jack Simth]

One problem with a computer run society is that, eventually, a successful cracker will come along and change things to his/her liking (and/or ruin the lives of others). Or do you truly believe someone will invent the perfect computer program? Especially when SOMEBODY has to have access to the hardware?

In a hogepodge (many different reasonably independant nations, many different reasonably independant systems) if something goes horribly, horribly wrong with one government, or one form of government, people can escape to the others (well, unless one "succeeds" in nuking everything, or similar), which can cause the collapse of the form that went horribly wrong (not necessarily directly - if a refugee starts a war that ends the regime (s)he fled, that indirectly caused the collapse (for loose definitions of collapse)); even if push comes to shove, in a hogepodge, things are recoverable even with extremely high levels of corruption.

A fully encompassing government, however, doesn't have a repair mechanisim that can operate on that level. Of necessity, a fully encompasing government needs to be held to a much, much higher standard - to the point of true perfection; which isn't really possible in something run by humans as they are, or as they will be within the foreseeable future.