From “What is Capitalism?” in Ayn Rand’s Capitalism: The Unknown Ideal.
“The common good” (or “the public interest”) is an undefined and undefinable concept: there is no such entity as “the tribe” or “the public”; the tribe (or the public or society) is only a number of individual men. Nothing can be good for the tribe as such; “good” and “value” pertain only to a living organism—to an individual living organism—not to a disembodied aggregate of relationships. . . .
When the “common good” of a society is regarded as something apart from and superior to the individual good of its members, it means that the good of some men takes precedence over the good of others, with those others consigned to the status of sacrificial animals. It is tacitly assumed, in such cases, that “the common good” means “the good of the majority” as against the minority or the individual. Observe the significant fact that that assumption is tacit: even the most collectivized mentalities seem to sense the impossibility of justifying it morally. But “the good of the majority,” too, is only a pretense and a delusion: since, in fact, the violation of an individual’s rights means the abrogation of all rights, it delivers the helpless majority into the power of any gang that proclaims itself to be “the voice of society” and proceeds to rule by means of physical force, until deposed by another gang employing the same means.
You can also listen to an audio version of this article Ayn Rand delivered at Ford Hall Forum in 1967.