unfortunately greed, jealousy, and lies come into play and wreak havoc in everything
I think a slight difference between the needs and interests of people are enough wreak havoc. Even if we take all the "bad" things from the human nature, individuals will get into conflicts even with the best intentions. That's why I think possession is a good thing, and that there won't be world piece without strong controlling power(s) with all its trade-offs (I'm talking about practical things, like a government, not God) or a much more sparse distribution of humans. Or some global heroine-like drug, or Matrix.