As with most things, it's a matter of the heart.
As a matter of economics, there is the kind of greed that plays a real and useful function in the marketplace. It inspires ideas, risks, hard work, efficient work, and responsiveness to markets. On a large scale and a reasonably fair playing field, it very much results in the betterment of all to some degree. This kind of greed does not require a heart disdainful of the needs of others. Indeed, watch Shark Tank and you see some entrepeneurs whose heartfelt goal is to provide jobs in areaa devestated by economic dislocation. Even when less altruistic, greed devoid of malice can still prove beneficial. And the U.S. is proof that all five of the beneficial qualities listed above can result in an economy which provides real, long-lasting security benefits for a country.
Of course we've all seen the kind of heart that seeks only to indulge itself in more and more pleasure, more and more self-worship, with a disdain that the effect on others is utterly immaterial. This latter is the real putoff.
So there's economic greed, and then there's personal greed. The latter is the dangerous one.
The real subject, and the real driver of economic jealousy is the sense among working people in the modern world is that (1) the game has been increasingly rigged in favor of large corporations and connected people that are (2) increasingly remote from their lives. It's true that one can point to the exact same things throughout history, but many people feel the degree of large and the degree of remoteness has become intolerable. What they feel is not directly influenced by the context of history. They just know that "those in charge" aren't bothering to truly listen and respond to their concerns.
The racial underclass (Black Lives Matter, for example) includes this but adds many other extreme grievances and frustrations. My personal opinion is that many of the grievances have some legitimacy, but too many of their cultural leaders follow a quasi-Marxist ideology that is much better at destroying than it is building.
Much more here to ponder than I have energy or time to spend, but to me income inequality is more tolerable when people feel they have some real chance at moving up a little.