Let's take a very prosperous society. Even if all people get wealthier (let's say 2x), which would mean improvement in life quality and all, and 10% of them get massively richer (let's say 20x), then we as a society still have a problem. Because it will be extremely hard for someone who is in the bottom part to get to the upper one. Because of numerous reason I could elaborate on: they will not be able to afford the same schooling, or be in the same expensive circles which creates the networking opportunities. Numerous studies show growing inequality reduces social mobility (American Dream, where are you?). Sure, a couple persons will prove that wrong, but statistics are here.

So at some point, inequality is in itself a problem, even if everyone has enough to eat and more. Because everybody should have chances at succeeding - that is, changing things, but also taking responsibilities. PG means often that being a hacker is enough and you can change a lot with that only, but I think this is not enough. CEOs, judges, bankers, politicians should come from a diverse background. And you don't get there without some equality.

And don't get me started on inheritance ;)