We have no disagreement on the definition of true socialism. Where the difference lies is in our understanding of the true base desires of natural human behavior. Yes, humans are social because we learn quickly that it is easier and more pleasant to survive in cooperation with others. This doesn’t change the basic selfish desires we have but in fact supports selfish desires at a more intellectual level.
Our culture is full of examples. We go to work, not because we enjoy what we do but, because we want the personal reward every two weeks. We work harder when the opportunity for recognition or advancement is present. Corporations advertise because they want a larger share of the market. We want, we want, we want. The more we want, the more we are willing to work for it. This is what makes a capitalistic society work.
It is also what makes socialist societies fail. The lists of freeloaders are long in the welfare/dole systems around the world. Many actually consider it their right to receive money from these systems without the responsibility of adding to the system. The shorter list is the one of manipulators who usurp the power within the system for their personal gain. Regardless of the method of abuse, one, but usually both, prevent the establishment of a true socialist society.
It is inarguable that socialism cannot survive the presence of greed/selfishness.