What is "human nature," anyway? All we can really comment on is how humans, as a whole, act within a capitalist mode of production. Any other statements about what human nature prohibits, or leads to, is pure speculation.
I see a lot of people suggesting the thing inherent to human nature that makes socialism "great on paper, good in theory" or whatever other liberal bullshit is greed, or self interest. Greed is a byproduct of wealth accumulation; in a society where worker's retain the surplus value created by their labor, the ability to act upon greed is GREATLY restricted, and, in higher-stage communism, cannot exist, as money has been abolished.
Self-interest, however, is something that is mostly divorced from economic systems. While one can theorize about how capitalist socialization results in selfishness, and decreases altruism, we really don't know to what extent this exists. So the question remains about whether or not socialism would be in the self-interest of the majority of the population.
On the surface, socialism is, quite obviously "better" than capitalism; through the elimination of wage labor and private property, economic exploitation is lowered, and people retain the (majority, as publicly-funded programs would require some allocation of labor) of the value they produce.
Capitalists argue that capitalism incentives innovation, and as such, despite including exploitation not present in socialism, benefits the most amount of people, as even the exploited people supposedly benefit more from the extra wealth creation. However, when one analyzes this statement, it falls apart. In socialism, where value is determined by the labor used, advancements in efficient production methods is obviously an important issue, and a something that would be focused on. Under capitalism, innovation and advancement are not driven by increasing production efficiency and reducing the labor required, but instead by profit. The capitalist mode of production inherently devalues labor. If it is cheaper to continue with an inefficient production method, paying laborers next to nothing, than taking the time and effort, and resources, to innovate, then they WILL do this. This issue is only magnified in a global economy, where labor can be outsourced to third world countries, where capitalists are able to pay wages of mere pennies an hour.
Hope this can help explain my view of the situation. If anybody sees any errors I've made, or has any comments, I would appreciate it, as I am still learning, and somewhat new to socialism/communism as a whole.