Originally posted by transio
You're comparing totally unrelated entities. How does diversity make government better? Diversity in business, technology, genetics is a good thing, but in government???
First off, you mentioned the Euro. That is something other than government - a number of countries have directly tied the value of their money to the US dollar, which is almost the same thing (except the balance between the dollar and pesos or the yen is a bit more uneven than the euro's distribution of influence). Single economic systems can crash and crash hard. We are already part way there today even without a unified currency. Remember the hedge fund bailout a couple of years ago, the one that was so overly leveraged we would have probably seen a real, old-style, but world-wide, recession if it had not been bailed out?

As for arguing against a unified government, that is trivially easy. One word that represents hundreds of similar situations on a smaller scale - Hitler. There's lot of other reasons having to do with centralized control, etc. But it all comes down to diversity breeds strength and resilience, monocultures do not, if fact I'd be willing to be that they can not. Although proving a negative is always difficult if not impossible. Disproving it isn't.