Why???

Why does it exist that we have a system where we group people into categories of who is of the caste of interacting with who?  I think that would be a bit touchy.  I am usually in a good caste, so I feel sorry for the others.  In the end, people explode and say that the only reason they have problems is because they were treated unfairly, and then if they don't think your race is white enough they hurt you for being more privileged.