I have to say I'm confused by the debate in this thread. Surely the scope of a government has little to do with its effectiveness at defending the civil rights and liberties of the population. Is the government of Finland (pop. 5 million) less effective at this than the federal government of the United States (pop. 300 million)? Likewise, if Russia attacks and annexes Finland (past performance notwithstanding) surely we wouldn't then say that Finland wasn't a legitimate political entity before then because it couldn't defend itself against a much larger enemy.
I should back up for a minute. Liberal arguments about the necessity of centralized government are always marshalled in the defense of Reconstruction or civil rights legislation of the 1960s. But this is a case of constructing an argument around a positive conclusion and calling it a good argument. It isn't necessarily so. Cheering on federal troops for enforcing civil rights laws in Mississippi seems like a short stop on the liberal-humanitarian ladder from declaring that we must bomb the women of Afghanistan to liberate them.
Political entities are not immutable, they're just human creations. The Confederacy was created to defend slavery, of course, but what if the balance of power had been slightly tilted the other way? What if Northern states had been fed up at being bullied by the over-represented slave states and decided to take their toys and go home? Would that also have been "treasonous?" What if Vermont decided to secede? Is that also a stronghold of Bubba redneckism that has to be reigned in by the virtuous federal government? The argument, apparently, is that the more diverse the population governed, the more likely the government will have to recognize the rights of minorities to survive. I don't think that's convincing or that it's really borne out by history, and not just the most famous example but United States history as well.
On the flip side, of course, there's nothing inherently righteous about decentralization either. Many rural areas in the United States are ossified class societies effectively run as neofeudalist fiefdoms by a handful of dynastic landlords. The democratic legitimacy of a government has little to do with the number of people governed but the nature of the power represented by that government.