Two things refute this:Again, I'm not defending the Empire here so much as illustrating that I see nothing positive about the Old Republic, given that it is constantly bashed in Episodes I and II. So, I do not see why anyone would logically wish to hand the reigns of power back to those who ruled an already failed political system.
1. You are assuming that the New Republic will be just like the old Republic, warts and all. Just because the Old Republic was corrupt and a bad thing, it doesn't mean that the Rebellion/New Republic would be as well. The Old Republic worked pretty well for several thousand years, it was just recently (in SW-time) that it went astray. The Rebellion, for all we know, could have been espousing a Jeffersonian "rewrite the constitution every generation" approach or another method of fixing the problems of the old Republic.
2. Luke is an idealist. He and Han are clearly opposites: Han is the mercenary with no loyalty to anyone but himself and his wallet, Luke is the naive kid. Luke saves Princess Leia because he thinks she's hot and she's a damsel in distress. Han does because he'll get a reward. Whatever flaws the Rebellion/New Republic had, Luke may not have seen them at that point. And, even if he had, like any good idealist, better hte possible harm in the future than the known harm in the present.
This would only be a problem if the "four planets" you complain about comes about because of mere coincidence. Anakin's "immaculate conception" backstory pretty clearly indicates that there is a lot more than mere coincidence at work. You might as well complain that Bilbo stumbled onto the One Ring and just so happened to pass it on to his cousin who was friends with the gardener and the two of them together had just the right combination of luck, pluck and courage to see the Quest through to the end. The prophecy that Anakin will bring balance to the force or whatever drives it is prima facie proof that characters are being used by some greater power to achieve an end.This just illustrates my point about the four planet universe of Star Wars, and the fact that everyone must know everyone.