One of the premises of the justification of what is called the “Collectivist Fallacy” (as I understand it) is that society is merely an aggregate of individuals engaged in exchanges for mutual benefit. The consequence is that society as such as no purpose, because all purposiveness of society is reducible to individuals. However, this presupposes certain metaphysical errors.
First, we may consider principals of unity, that is the source of the oneness of a thing. Unity may be intrinsic, extrinsic or merely conventional. An intrinsic prinpical of unity gives rise to a substantial unity. An extrinsic principal gives rise to an accidental unity. A merely convention unity gives rise to an aggregate.
A substantial unity is a substance such as an animal. An animal is unified as a whole by its intrinsic telos. It seeks its own perfection and is unified in this purpose; every part of the whole seeks that end. An important realization is that even if every part of the the whole is replaced it remains itself. Over the course of a lifetime all of the most basic parts of an animal are replaced by different parts, however, the whole remains the same thing. It remains the same animal and individual.
An aggregate is called one or a whole solely based on convention. Consider a collection of rocks. There is no principal of unity and it is merely called a unity by convention, that is it is one “collection” though there is no principal of unity that actually unifies it. As distinct from a substantial unity, if we replace each part of the whole, then we have a different collection or whole. The collection of rocks is merely the sum of its parts.
An accidental unity in contrast to a substantial unity does not have an intrinsic unity and is not a substance. It does not exist in and of itself. However, it is unified in a way that an aggregate is not. A chair is of this sort. A chair is not merely an aggregate of wood, because it does have a purpose and telos, that is for sitting, but this is extrinsic. That is the chair as made of wood has the intrinsic principal of becoming a mature tree, but the extrinsic telos is for sitting. In this, we can repair the chair over time, replacing each piece, and the chair rmeains the same chair.
This final sort of unity is the most controversial. Aristotle talks about the problem of a ship as an accidental unity and discusses the problem of replacing every part of it. However, we may consider here the unity of the state and society. It is clearly incorrect that the state is a substantial unity. It does not exist as a substance in and of itself. However, it is also not merely an aggregate. If every part of the state, i.e. the people, is replaced it remains the same state.
The state is thus an accidental unity. It does have a principal that unifies it and this is the reason for the stability of state in spite of all of the parts changing. The unifying principal is the common good, which is the good shared by many. The state then does have some purpose and end that is moves toward. This is a metaphysical position, because the state would not exist at all as a unified whole did it not have some telos.
We may discuss what the common good is, but the collectivist fallacy presupposes this in acknowledging the that men gather together for exchanges for mutual benefit. If that is the case, then the state and society exist to meet the conditions necessary for good exchanges of mutual benefit and the exchanges of mutual benefit are themselves concerned with the common good. These good exchanges are the reason that society exists, that is why men come together and form society. Like an animal that is starving, i.e. not meeting the conditions for health and life, a society that does not work toward meeting that end will begin to disintegrate.