There can't be "liberty for some" in a country without problems. That's not liberty. There either is liberty or there isn't. Even France had "liberty for some" before the revolution, but obviously liberty and equality must be for everyone. The fact that the USA considered slaves as "not persons" legally was only a political escamotage to allow legal infringement of liberty, because obviously the political class was voted by those who were becoming rich with slaves, and not by slaves who had no rights to vote. Note how the right to vote is also connected to this. Now, yes it is possible for a country to "run" such civics at the same time, but with obvious problems which increase with the size of the "oppressed population" (let's forget of silly arguments like "a slave cannot wish to vote if he never voted, please -_-"). This happened throughout history in any country or system you can think of, from Spartacus to Bastille and Martin Luther King. In Civ terms this can be translated very well by rising unhappyness if you run a civic which grants liberties to population together with one that takes away liberties from the population.