"humans are built for sharing, not greed". According to who? It may sound good but I don't see supporting evidences for that in history, archaeology, biology or even basic self-interest.

Greed is natural part of the human experience, what is important is how do we make sure that the greed of one actually benefit the other. Anyone who proclaims that we should do away with it has some dangerous totalitarian streak in their personality. Humans can't be molded like play dough and if you try, you'll have to use the power of the gun or the treat of violence.

Sharing is not always a virtue, if it's not reciprocal, you can actually incentivize dependency and decentivize self-reliance. You can also share something harmful with someone like drugs, a cigarette or bad habits for that matter.