Copied and pasted again:

Human nature arguments boil down to the fact that the ruling ideology of society is shaped by the base economic relations. In other words, we perceive it as "natural" to work for monetary incentives because that's pretty much the only choice we have right now. It seems "natural" that there should be hierarchy because we have them at our jobs, in our democracy, in the home thanks to patriarchal family relations, etc. Humans seem greedy "by nature" because without money, we starve or can't pay for shelter, so it is in our interest to try to accumulate money in under the current economical setup. Capitalism literally compels capitalists to behave in a way that can be perceived as greedy, because if they don't, their competitor will and then they will be gobbled up or put out of business. It's the system that makes these things seem natural or essential.

But Engels and Marx and others disproved these things about human nature by looking at history. Among many native nations in the Americas, there was no money. How, then, did anything get done if money is the only incentive to work? There is also a ton of evidence that humans, for millions of years, operated more or less communally, with little or no hierarchy. If it was innate "human nature," how could this be so? How could greedy humans cooperate and survive during these millions of years of scarcity if they were all so greedy and purely self-interested by nature?

To attribute contemporary human behavior to "human nature" without looking at history and without considering the effects of the environment and social relations that necessarily shape human behavior is simplistic and unscientific, and it is usually an excuse made by the politically faint of heart or those who benefit from the current economic system.

I would point out that there is a massive propaganda effort to control this narrative and force it into our minds. But real heart of the matter, that Marx would tell you, is that it is because the system (capitalism) forces those conditions upon you. In order to succeed in capitalism, it often pays off to behave greedily, and many situations arise where to not behave greedily is to fall behind and risk losing. And to lose in capitalism is to be made a debt slave, if not then to be homeless, broken, hungry, and in a word, oppressed. And here's where Marx ideas get really powerful. If you want to change this behavior - to act greedily - then you need only change the system that the person is in. If you have a system (socialism), where you will always have a home, always have food, always have medical care, always have water - then there is no need to behave greedily in order to survive and have a life of dignity and purpose. Marx would argue that greed will pass from the human condition. Poverty and war too. This was Karl Marx's dangerous idea - you wouldn't just change the world, but all of humankind.