The vast majority of people need to give in order to be truly happy. The rare disabled/ill/elderly person who doesn't want to give anything isn't going to disrupt the entire system or radically change human nature. You clearly have never lived in a commune.
Humans are generally very giving, we evolved in communities and we had to be generous and kind to others. But now is a completely different ball game, the people in power have amassed vast amounts of wealth when they would of been the type to have been outcasts from their tribes.