I really don't care to get into the human nature argument, so I'll for the most part agree to disagree here since this is one that tends to just go in circles forever. That being said greed in humans is not human nature any more than that it has been bred into our species. "Human nature" is nothing more than common attributes of humans as a result of the social and material conditions of a society, at least that is the Marxist perspective on the issue. I mean, everyone else's stances are pretty clear here, I just want to throw mine out there
But there seems to be a bit of a misconception here, communists in general and I don't think Oscad either was suggesting that with the social attitudes present today you could make communism work. That has been tried various times ie in the case of the Spanish civil war, Paris commune, and early utopian socialists and proven to be a disaster each time. Part of the entire purpose of the dictatorship of the proletariat and withering away of the state though is for a state controlled by the working class to manage the social antagonisms that would prevent communism from working until they are rare enough that you could realistically have a stateless society. Sure, when push comes to shove individual humans will act in the interest of their survival, but that would scarcely be necessary in a post-scarcity or mostly automated society.