First, if any opinion is compelled to silence, that opinion may, for aught we can certainly know, be true. To deny this is to assume our own infallibility. Secondly, though the silenced opinion be an error, it may, and very commonly does, contain a portion of truth; and since the general or prevailing opinion on any subject is rarely or never the whole truth, it is only by the collision of adverse opinions, that the remainder of the truth has any chance of being supplied. Thirdly, even if the received opinion be not only true, but the whole truth; unless it is suffered to be, and actually is, vigorously and earnestly contested, it will, by most of those who receive it, be held in the manner of a prejudice, with little comprehension or feeling of its rational grounds. And not only this, but, fourthly, the meaning of the doctrine itself will be in danger of being lost, or enfeebled, and deprived of its vital effect on the character and conduct: the dogma becoming a mere formal profession, inefficacious for good, but cumbering the ground, and preventing the growth of any real and heartfelt conviction, from reason or personal experience.

The peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.

First, if any opinion is compelled to silence, that opinion may, for aught we can certainly know, be true. To deny this is to assume our own infallibility. Secondly, though the silenced opinion be an error, it may, and very commonly does, contain a portion of the truth; and since the general or prevailing opinion on any subject is rarely or never the whole truth, it is only by the collision of adverse opinions that the remainder of the truth has any chance of being supplied.

the English philosopher John Stuart Mill argued that silencing an opinion is “a peculiar evil.” If the opinion is right, we are robbed of the “opportunity of exchanging error for truth”; and if it’s wrong, we are deprived of a deeper understanding of the truth in “its collision with error.

But the peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.” — John Stuart Mill1

In his celebrated little book On Liberty, the English philosopher John Stuart Mill argued that silencing an opinion is “a peculiar evil.” If the opinion is right, we are robbed of the “opportunity of exchanging error for truth”; and if it’s wrong, we are deprived of a deeper understanding of the truth in “its collision with error.” If we know only our own side of the argument, we hardly know even that; it becomes stale, soon learned only by rote, untested, a pallid and lifeless truth.

Half a truth is often a great lie

When truth is divided, errors multiply.

That a lie which is half a truth is ever the blackest of lies;
That a lie which is all a lie may be met and fought with outright;
But a lie which is part a truth is a harder matter to fight.

Thought that is silenced is always rebellious. Majorities, of course, are often mistaken. This is why the silencing of minorities is necessarily dangerous. Criticism and dissent are the indispensable antidote to major delusions.

As Leslie Stephen has demonstrated, to suppress one truth is to suppress all truth, for truth is a coherent whole.

Only those afraid of the truth seek to silence debate, intimidate those with whom they disagree, or slander their ideological counterparts. Those who know they are right have no reason to stifle debate because they realize that all opposing arguments will ultimately be overcome by fact.

The greatest enemy of any one of our truths may be the rest of our truths

It is not difficult to deprive the great majority of independent thought. But the minority who will retain an inclination to criticize must also be silenced....Public criticism or even expressions of doubt must be suppressed because they tend to weaken pubic support....When the doubt or fear expressed concerns not the success of a particular enterprise but of the whole social plan, it must be treated even more as sabotage.