Your vision of Middle Earth as a United Nations-style democracy is a disturbing one indeed; if there must be a one-world government, I'd prefer to think of it as a republic of autonomous 'states' (and as a good Southerner I believe these states should have the right to secede if they wish). I realize that 'I am Aragorn son of Arathorn, and am called Elessar, Chief Executive of Gondor' won't stir many hearts, but the price of liberty is high. :-)
To put in another two cents for home rule, Aragorn may well have issued an edict banning outside interference, but it was the local populace taking up arms against their oppressors that finally restored freedom to the Shire. Nothing quite like a little home-grown revolution!
Lest you think, however, that I tear through fantasy novels continually screaming "Death to the aristos!", I should say that I am a long-time fan of British literature and film, many of the best stories from which focus on the upper classes, so I certainly do understand the appeal. Don't take my libertarian opposition to the feudalism of LOTR too seriously!
And don't take my apparent support of aristocracy and condemnation of the democratic process too seriously either ;~D Of course we could support Aragorn as King... He came by it through hard work and heroism (and he is good lookin')... But his kids would be horrid spoiled heirs that would need to be overthrown.