In exploring Ayn Rand’s Objectivism, I found this:
When one speaks of man’s right to exist for his own sake, for his own rational self-interest, most people assume automatically that this means his right to sacrifice others. Such an assumption is a confession of their own belief that to injure, enslave, rob or murder others is in man’s self-interest—which he must selflessly renounce. The idea that man’s self-interest can be served only by a non-sacrificial relationship with others has never occurred to those humanitarian apostles of unselfishness, who proclaim their desire to achieve the brotherhood of men. And it will not occur to them, or to anyone, so long as the concept “rational” is omitted from the context of “values,” “desires,” “self-interest” and ethics.
via Self-Interest — Ayn Rand Lexicon. Perhaps this might be restated as: a thinking individual’s interests are best served by positive, mutual cooperation with others.