A class system exists in every society as long as the society looks anything like ours. I doesn't need to be programmed in.

However it could be programmed out... but taxation tiers is never the only sign of such a society. Instead some families are higher educated, they have solar panels on their roofs, they live in safer areas, they drive a nicer cars, their kids go to a better schools... some families are not like that, but instead, as an example, live in a small apartment, in a tower block next to the water treatment plant.