We are on the one hand kind, generous, and sympathetic; on the other, competitive, self-interested, and prone to cruelty.
We are both and all of these things, with divided natures: human, but also animal; social, but also individualistic; empathetic and generous, but also self-interested and jealous.
Neither side is right or wrong, or good or evil; both are essential aspects of human nature. There is nothing we can do about them even if we wanted to.
Capitalism, libertarianism, nationalism, and similar impulses can be thought of as mass analogues to the individualistic side of human nature. We naturally want to succeed, for ourselves and our families (our genes). We band together into clans, states, nations, and apply our individual sense of self-vs.-other to these group identities as well. We want to be in charge of our own destinies, as individuals and as polities. In pursuit of these goals, it's natural to want freedom and liberty. We don't want government, or any kind of larger force, to be telling us — whichever "us" we are talking about — what to do. We want to be free to succeed or fail on our own merits. And so we have invented capitalism, and developed ideologies and policies that support it.
At the same time we want to live in a harmonious world. The natural sympathy characteristic of our social side makes us want others to be happy too — sometimes making us go so far as to feel a need to help the unfortunate who cannot even return the favor. We tend to shrink from cruelty and violence. At the least — assuming we are not sociopaths or Ayn Rand — we find unadulterated selfishness distasteful. And so we have created moral doctrines based on love and harmony; social programs reflecting these doctrines; and organizations dedicated to peace.