The Revelation of the Ancient Kingdom would be meaningless for most of the People around the world, from simple Farmers who struggle to meet the months end to the Kings and Queens who rule Islands, None of them would really care About a lost Kingdom from 800 years ago. Even than we can't Judge the CD für the crimes of there ancestors (Maybe Imu and the Gorosei if they are truly over 800 yo), Roger said we shouldn't punish a child for the sins of his parents, we can only punish the CD for there actual crimes in present.
And if the CD are down many greedy Kings, Emporers and other Rulers would fight the get the same power as the CD, war would break out and many lives would be lost.
And if the Revolution army takes Control, how Long would Peace last? 1 year? 5 years? 10 years? In the end many corrupt members and oppurtonists would rise in power and take Control; in the end a fascist government would be replaced with a other fascist goverment.
In the end all the efforts of the revolutionary army would be wasted, for the naivety to belive in the good human nature. In the end Humans have boths sides and it's only a matter of time until the corruption manifest in the people hearts.