What human nature is and what it isn't has been a subject of much debate through the times, and it should be. We see in people capacities for all sorts of things. I am looking at the issue from the standpoint of simple rationality, and that is: A being that exists as himself, as part of humanity and as part of life will have orientation toward all the preceding, with different people having different mixes and at different times in their lives.
Suppressing either of the above leads to it manifesting sideways and destructively. In the Soviet Union, that denied self-interest, self-interest manifested as corruption. In 1980s America that denied humanity-interest, equating it with communism, humanity-interest also manifested sideways: As an oppressive demand for absolute similitude of belief, thought and behavior. And the denial of life-interest leads to a sick and destructive relationship with nature, in which people take from nature whatever they want and leave the rest to die.
These wrongs can only be righted by ending these attacks on humanity's natural potentials and giving them a positive outlet. With life-interest, people should be able to enjoy nature while taking care to leave it preserved. With humanity-interest, people should be able to take constructive action that benefits the world. And with self-interest, people should be able to have a meaningful choice of lifestyles in which they get to decide, meaningfully, what life they can live.
Neither self-interest nor altruism nor life-interest are good or evil. They are part of what we as people are. If either potential gets suppressed, the results are destructive. If either potential becomes monopolistic, the results are destructive as well.
The great minds in psychology, philosophy and religion all claim to have the truth. What they have is part of the truth. They see a part of the human nature but confuse it with its totality. And it is by seeing the human nature in its entirety and acting accordingly that real benefit can be achieved for humanity, for nature, and for individual human beings who live on Earth.