Yes, we've upheld one but it's a multi layered, incredibly complex thingymabobby (and yes, that is the technical term) which no one can claim to completely understand. It's largely subjective, as seen by the "Am I MC/WC?" threads on here.
So really, we have a CONCEPT of class, which impacts everybody and which no one can completely define. But it's not like the caste system or feudal system.