On Liberty by John Stuart Mill (1806-1873) is one of the founding texts of modern liberalism. In the extracts below, Mill first sets out his general thesis - that the government and society should only restrict individual freedom in order to prevent harm from being done to others - and then goes on, in discussing the legitimacy of freedom of expression, to explain the difficulty involved in claiming that any given system of belief, even one which represents the conventional wisdom, is undeniably true.
There is, in fact, no recognized principle by which the propriety or impropriety of government interference is customarily tested. People decide according to their personal preferences. Some, whenever they see any good to be done, or evil to be remedied, would willingly instigate the government to undertake the business; while others prefer to bear almost any amount of social evil, rather than add one to the departments of human interests amenable to governmental control. And men range themselves on one or the other side in any particular case, according to this general direction of their sentiments; or according to the degree of interest which they feel in the particular thing which it is proposed that the government should do; or according to the belief they entertain that the government would, or would not, do it in the manner they prefer; but very rarely on account of any opinion to which they consistently adhere, as to what things are fit to be done by a government. And it seems to me that, in consequence of this absence of rule or principle, one side is at present as often wrong as the other; the interference of government is, with about equal frequency, improperly invoked and improperly condemned.
The object of this Essay is to assert one very simple principle, as entitled to govern absolutely the dealings of society with the individual in the way of compulsion and control, whether the means used be physical force in the form of legal penalties, or the moral coercion of public opinion. That principle is, that the sole end for which mankind are warranted, individually or collectively in interfering with the liberty of action of any of their number, is self-protection. That the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others. His own good, either physical or moral, is not a sufficient warrant. He cannot rightfully be compelled to do or forbear because it will be better for him to do so, because it will make him happier, because, in the opinions of others, to do so would be wise, or even right. These are good reasons for remonstrating with him, or reasoning with him, or persuading him, or entreating him, but not for compelling him, or visiting him with any evil, in case he do otherwise. To justify that, the conduct from which it is desired to deter him must be calculated to produce evil to some one else. The only part of the conduct of any one, for which he is amenable to society, is that which concerns others. In the part which merely concerns himself, his independence is, of right, absolute. Over himself, over his own body and mind, the individual is sovereign.
It is, perhaps, hardly necessary to say that this doctrine is meant to apply only to human beings in the maturity of their faculties. We are not speaking of children, or of young persons below the age which the law may fix as that of manhood or womanhood. Those who are still in a state to require being taken care of by others, must be protected against their own actions as well as against external injury. For the same reason, we may leave out of consideration those backward states of society in which the race itself may be considered as in its nonage.... Despotism is a legitimate mode of government in dealing with barbarians, provided the end be their improvement, and the means justified by actually effecting that end. Liberty, as a principle, has no application to any state of things anterior to the time when mankind have become capable of being improved by free and equal discussion.... But as soon as mankind have attained the capacity of being guided to their own improvement by conviction or persuasion (a period long since reached in all nations with whom we need here concern ourselves), compulsion, either in the direct form or in that of pains and penalties for non-compliance, is no longer admissible as a means to their own good, and justifiable only for the security of others.
In order more fully to illustrate the mischief of denying a hearing to opinions because we, in our own judgment, have condemned them, it will be desirable to fix down the discussion to a concrete case; and I choose, by preference, the cases which are least favourable to me - in which the argument against freedom of opinion, both on the score of truth and on that of utility, is considered the strongest. Let the opinions impugned be the belief in a God and in a future state, or any of the commonly received doctrines of morality. To fight the battle on such ground, gives a great advantage to an unfair antagonist; since he will be sure to say (and many who have no desire to be unfair will say it internally), Are these the doctrines which you do not deem sufficiently certain to be taken under the protection of law? Is the belief in a God one of the opinions, to feel sure of which, you hold to be assuming infallibility? But I must be permitted to observe, that it is not the feeling sure of a doctrine (be it what it may) which I call an assumption of infallibility. It is the undertaking to decide that question for others, without allowing them to hear what can be said on the contrary side. And I denounce and reprobate this pretension not the less, if put forth on the side of my most solemn convictions. However positive any one's persuasion may be, not only of the falsity, but of the pernicious consequences--not only of the pernicious consequences, but (to adopt expressions which I altogether condemn) the immorality and impiety of an opinion; yet if, in pursuance of that private judgment, though backed by the public judgment of his country or his contemporaries, he prevents the opinion from being heard in its defence, he assumes infallibility. And so far from the assumption being less objectionable or less dangerous because the opinion is called immoral or impious, this is the case of all others in which it is most fatal. These are exactly the occasions on which the men of one generation commit those dreadful mistakes which excite the astonishment and horror of posterity. It is among such that we find the instances memorable in history, when the arm of the law has been employed to root out the best men and the noblest doctrines; with deplorable success as to the men, though some of the doctrines have survived to be (as if in mockery) invoked, in defence of similar conduct towards those who dissent from them, or from their received interpretation.
Mankind can hardly be too often reminded, that there was once a man named Socrates, between whom and the legal authorities and public opinion of his time, there took place a memorable collision. Born in an age and country abounding in individual greatness, this man has been handed down to us by those who best knew both him and the age, as the most virtuous man in it; while we know him as the head and prototype of all subsequent teachers of virtue, the source equally of the lofty inspiration of Plato and the judicious utilitarianism of Aristotle, "i maestri di color che sanno," the two headsprings of ethical as of all other philosophy. This acknowledged master of all the eminent thinkers who have since lived - whose fame, still growing after more than two thousand years, all but outweighs the whole remainder of the names which make his native city illustrious - was put to death by his countrymen, after a judicial conviction, for impiety and immorality. Impiety, in denying the gods recognized by the State; indeed his accuser asserted (see the "Apologia") that he believed in no gods at all. Immorality, in being, by his doctrines and instructions, a "corrupter of youth." Of these charges the tribunal, there is every ground for believing, honestly found him guilty, and condemned the man who probably of all then born had deserved best of mankind, to be put to death as a criminal.
To pass from this to the only other instance of judicial iniquity, the mention of which, after the condemnation of Socrates, would not be an anti-climax: the event which took place on Calvary rather more than eighteen hundred years ago. The man who left on the memory of those who witnessed his life and conversation, such an impression of his moral grandeur, that eighteen subsequent centuries have done homage to him as the Almighty in person, was ignominiously put to death, as what? As a blasphemer. Men did not merely mistake their benefactor; they mistook him for the exact contrary of what he was, and treated him as that prodigy of impiety, which they themselves are now held to be, for their treatment of him. The feelings with which mankind now regard these lamentable transactions, especially the latter of the two, render them extremely unjust in their judgment of the unhappy actors. These were, to all appearance, not bad men - not worse than men most commonly are, but rather the contrary; men who possessed in a full, or somewhat more than a full measure, the religious, moral, and patriotic feelings of their time and people: the very kind of men who, in all times, our own included, have every chance of passing through life blameless and respected. The high-priest who rent his garments when the words were pronounced, which, according to all the ideas of his country, constituted the blackest guilt, was in all probability quite as sincere in his horror and indignation, as the generality of respectable and pious men now are in the religious and moral sentiments they profess; and most of those who now shudder at his conduct, if they had lived in his time and been born Jews, would have acted precisely as he did. Orthodox Christians who are tempted to think that those who stoned to death the first martyrs must have been worse men than they themselves are, ought to remember that one of those persecutors was Saint Paul.
Let us add one more example, the most striking of all, if the impressiveness of an error is measured by the wisdom and virtue of him who falls into it. If ever any one, possessed of power, had grounds for thinking himself the best and most enlightened among his contemporaries, it was the Emperor Marcus Aurelius. Absolute monarch of the whole civilized world, he preserved through life not only the most unblemished justice, but what was less to be expected from his Stoical breeding, the tenderest heart. The few failings which are attributed to him, were all on the side of indulgence: while his writings, the highest ethical product of the ancient mind, differ scarcely perceptibly, if they differ at all, from the most characteristic teachings of Christ. This man, a better Christian in all but the dogmatic sense of the word, than almost any of the ostensibly Christian sovereigns who have since reigned, persecuted Christianity. Placed at the summit of all the previous attainments of humanity, with an open, unfettered intellect, and a character which led him of himself to embody in his moral writings the Christian ideal, he yet failed to see that Christianity was to be a good and not an evil to the world, with his duties to which he was so deeply penetrated. Existing society he knew to be in a deplorable state. But such as it was, he saw or thought he saw, that it was held together and prevented from being worse, by belief and reverence of the received divinities. As a ruler of mankind, he deemed it his duty not to suffer society to fall in pieces; and saw not how, if its existing ties were removed, any others could be formed which could again knit it together. The new religion openly aimed at dissolving these ties: unless, therefore, it was his duty to adopt that religion, it seemed to be his duty to put it down. Inasmuch then as the theology of Christianity did not appear to him true or of divine origin; inasmuch as this strange history of a crucified God was not credible to him, and a system which purported to rest entirely upon a foundation to him so wholly unbelievable, could not be foreseen by him to be that renovating agency which, after all abatements, it has in fact proved to be; the gentlest and most amiable of philosophers and rulers, under a solemn sense of duty, authorized the persecution of Christianity. To my mind this is one of the most tragical facts in all history. It is a bitter thought, how different a thing the Christianity of the world might have been, if the Christian faith had been adopted as the religion of the empire under the auspices of Marcus Aurelius instead of those of Constantine. But it would be equally unjust to him and false to truth, to deny, that no one plea which can be urged for punishing anti-Christian teaching, was wanting to Marcus Aurelius for punishing, as he did, the propagation of Christianity. No Christian more firmly believes that Atheism is false, and tends to the dissolution of society, than Marcus Aurelius believed the same things of Christianity; he who, of all men then living, might have been thought the most capable of appreciating it. Unless any one who approves of punishment for the promulgation of opinions, flatters himself that he is a wiser and better man than Marcus Aurelius - more deeply versed in the wisdom of his time, more elevated in his intellect above it - more earnest in his search for truth, or more single-minded in his devotion to it when found; - let him abstain from that assumption of the joint infallibility of himself and the multitude, which the great Antoninus made with so unfortunate a result.