Here's another little bit from "Justice," which immediately follows the last passages linked. In it, Proudhon explains how, in the very early phases of the "shock of ideas," property emerged as a social convention precisely because human beings had not yet learned to question their own absolutism. Elsewhere, however, he makes it clear that our "absolutism" is not simply something we need to "get over" or grow out of, but an important enabling component in ethical evolution. This is part of the revision of the material Rafael posted, once Proudhon had decided that the antinomies did not resolve themselves.
There is some really elegant anarchist philosophy in this stuff - very challenging, but also very plumb-line in its way, without sacrificing either the individual or the social.
"Let us consider what occurs in the human multitude, placed under the empire of absolutist reason, so long as the struggle of interests and the controversy of opinions does not bring out the social reason.
"In his capacity as absolute and free absolute, man not only imagines the absolute in things and names it, which first creates for him, in the exactitude of his thoughts, grave embarrassment. He does more: by the usurpation of things that he believes he has a right to make, that objective absolute becomes internalized; he assimilates it, becomes interdependent (solidaire) with it, and pretends to respect it as himself in the use that he makes of it and in the interpretations that it pleases him to make of it. Each, in petto, reasoning the same, it results, in the first moment, that the public reason, formed from the sum of particular reasons, differs from those in nothing, neither in basis nor in form; so that the world of nature and of society is nothing more than a deduction of the individual self (moi), a belonging of his absolutism.
"All the constitutions and beliefs of humanity are formed thus; at the very hour that I write, the collective reason hardly exists except in potential, and the absolute holds the high ground.
"Thus, by virtue of his absolute moi, secretly posed as center and universal principle, man affirms his domain over things; all the members of the State making the same affirmation, the principle of societary absolutism becomes, by unanimity, the law of the State, and all the theories of the jurists on the possession, acquisition, transmission, and and exploitation of goods, are deduced from it. In vain logic demonstrates that this doctrine is incompatible with the data of the social order; in vain, in its turn, experience proves that it is a cause of extermination for persons and ruin for States: nothing knows how to change a practice established on the similarity of egoisms. The concept remains; it is in all minds: all intelligence, every interest, conspire to defend it. The collective reason is dismissed, Justice vanquished, and economic science declared impossible." (Justice, Tome III, pp 99-100)