What made the protection of individual liberty so sacred to Mill? In his famous essay he declares that, unless men are left to live as they wish 'in the path which merely concerns themselves', civilization cannot advance; the truth will not, for lack of a free market in ideas come to light; there will be no scope for spontaneity, originality, genius, for the mental energy, for moral courage. Society will be crushed by the weight of 'collective mediocrity'. Whatever is rich and diversified will be crushed by the weight of custom, by men's constant tendency to conformity, which breeds only 'withered capacities', 'pinched and hidebound', 'cramped and warped' human beings. 'Pagan self-assertion is a worthy as Christian self-denial'. 'All the errors which a man is likely to commit against advice and warning are far outweighed by the evil of allowing others to constrain him to what they deem is good.’ The defense of liberty consists in the ‘negative’ goal of warding off interference. To threaten a man with persecution unless he submits to a life in which he exercises no choices of his goals; to block before him every door but one, no matter how noble the prospect upon which it opens, or how benevolent the motives of those who arrange this, is to sin against the truth that he is a man, a being with a life of his own to live. This is liberty as it has been conceived by liberals in the modern world from the days of Erasmus (some would say of Occam) to our own. Every plea for civil liberties and individual rights, every protest against exploitation and humiliation, against the encroachment of public authority, or the mass hypnosis of custom or organized propaganda, springs from this individualistic, and much disputed, conception of man.
The other is that men should seek to discover the truth, or to develop a certain type of character of which Mill approved - critical, original, imaginative, independent, non-conforming to the point of eccentricity, and so on - and that truth can be found, and such character can be bred, only in conditions of freedom. Both these are liberal views, but they are not identical, and the connection between them is, at best, empirical. No one would argue that truth or freedom of self-expression could flourish where dogma crushes all thought. But the evidence of history tends to show (as, indeed, was argued by James Stephen in his formidable attack on Mill in his Liberty, Equality, Fraternity) that integrity, love of truth, and fiery individualism grow at least as often in severely disciplined communities among, for example, the puritan Calvinists of Scotland or New England, or under military discipline, as in more tolerant or indifferent societies; and if this is so, Mill's argument for liberty as a necessary condition for the growth of human genius falls to the ground. If his two goals proved incompatible, Mill would be faced with a cruel dilemma, quite apart from the further difficulties created by the inconsistency of his doctrines with strict utilitarianism, even in his own humane version of it.
— Isaiah Berlin, Two Concepts of Liberty, 1958.
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