Western societies of that time were enthralled by the idea of mankind's perfectibility, his fated control over the natural world, ability to dominate chance and rationalize society.
Our state religion is effectively atheism, and the same atheistic mind that believes in the perfectibility of man starts by separating people between the good and the bad.
Those who believe in human progress without believing in perfectibility will seek the best for their fellow human beings without being tempted to enslave them.