The cast system of India is one of the worst systems i have ever herd of. The entire system is a complicated set of beliefs to trick poor people into being treated horribly, and not speak, or act out about it.
With a combination of belittling the untouchables on a daily bases, and teaching them to believe that good behavior will be rewarded after they die. The highborns have done a great job of tricking the untouchables into being cheap laborers(slaves) without the chains.
They tie in religion to scare the uneducated lower class people into submission, telling the untouchables if you are faithful and obedient you will come back in the next life, and your life will be better. By not letting the untouchables close to the highborns(because of pollution), the highborns have cut off the untouchables chance of a seeing that they are all the same people.
To me this system is just a bunch of smoke an mirrors to make the rich people richer and keep the poor people poor.