Sith = Totalitarian, oppressive, freedom-restricting dictatorship/oligarchy. Change can only happen through force of arms, maybe even civil war.
Republic = Democratic, semi-corrupt government, yet has an institutionalized system for changing their system to better adapt.
Are people really saying they'd rather live under the Empire? Where basic freedoms such as speech, freedom to protest, freedom to press, etc. are taken away and the citizens are practically playthings of the force-using aristocracy? Really?
In the prequel, people chose to let the Republic become Empire.