The idea is: no matter how far we'll go folks will always find a way to resent other folks. Prejudice is part of our biological programming.

I'd add that they also despise them because they had these things and squandered them, while Martians have to struggle to build their own world. So when Earthers take resources to feed a dying planet it's salt on the wound.

Envious of an open sky, running water and so on, certainly. Which is understandable.
Let me show you the deep raw passion of unbridled sexual frenzy. But Lucy im British