Peter Kropotkin, answered from the texts and cited to the page.
I am accused of an optimistic view of human nature, and I accept the description while rejecting the charge of naivety, for my optimism is not a wish but a conclusion from evidence. Look at what human beings actually build when they are left to build it: the medieval city with its guilds and charters, the village commune with its common land, the lifeboat association, the Red Cross, the learned society, the trade union, the thousand voluntary bodies through which people coordinate vast and complex undertakings without a master over them.1
Mutual aid is not an ideal I project onto humanity; it is the observable practice of humanity wherever the state and the market have not succeeded in stamping it out. The Hobbesian who tells me that without the policeman we should fly at each other's throats has mistaken the exception for the rule and the diseased condition, produced by centuries of domination and poverty, for human nature itself.
Men are neither angels nor wolves; they are social animals in whom the instinct of solidarity, bred by evolution and elaborated by history, is as real as self-interest and stronger where circumstances let it act. Anarchy does not require perfect men; it requires ordinary men freed from the institutions that set them against one another and given back the self-government they have practised in every age.
Whether it can be done at the scale of a modern society is a fair question — but it is a question of institutions and conditions, not of an incurable wickedness in the human heart that the evidence does not support.23
We have now to follow the further developments of the same ever-living tendency for mutual aid. Taking the village communities of the so-called barbarians at a time when they were making a new start of civilization after the fall of the Roman Empire, we have to study the new aspects taken by the sociable wants of the masses in the middle ages, and especially in the mediaeval guilds and the mediaeval city.Mutual Aid, pp. 154–155
In proportion as the obligations towards the State grew in numbers the citizens were evidently relieved from their obligations towards each other. In the guild and in mediaeval times every man belonged to some guild or fraternity two " brothers " were bound to watch in turns a brother who had fallen ill; it would be sufficient now to give one's neighbour the address of the next paupers' hospital.Mutual Aid, p. 228
"Were it not for Church and and State, free societies would have already conquered the whole of the immense domain of education. And, in spite of all difficulties, they begin to in- vade this domain as well, and make their influence already felt.Anarchism, Its Philosophy and Ideal
The feasibility objection is the oldest and most persistent criticism of anarchism, pressed by Hobbesian liberals (no order without a sovereign) and by Marxists (anarchism is utopian, it skips the material and organizational preconditions of a stateless society). Kropotkin's answer rests on the historical and biological evidence of Mutual Aid and on the detailed economic argument of Fields, Factories and Workshops. Partial historical tests — above all the anarchist collectives of the Spanish Revolution (1936-39) before their suppression — are contested evidence. Contemporary scholarship on the self-governance of common-pool resources (Elinor Ostrom's Governing the Commons, 1990) and on non-state order (James C. Scott) has given empirical support to the claim that people can and do coordinate complex cooperation without central coercion, though rarely at the scale anarchism envisions.