This quotation is taken from Karl Popper’s 1945 book, The Open Society and Its Enemies.

The text is taken from the end notes to Chapter 7, as indicated by the cite. I’ve taken the liberty of re-paragraphing it, as the original is one gigantic block of text, and (I find that) these chunks are hard to follow. I also add the bolded text for my own purposes; the italic fonts are in the original.

The so-called paradox of freedom is the argument that freedom in the sense of absence of any restraining control must lead to very great restraint, since it makes the bully free to enslave the meek. … Less well known is the paradox of tolerance: unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them.—In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be most unwise.

But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant. We should claim that any movement preaching intolerance places itself outside the law, and we should consider incitement to intolerance and persecution as criminal, in the same way as we should consider incitement to murder, or to kidnapping, or to the revival of the slave trade, as criminal.

Another of the less well-known paradoxes is the paradox of democracy, or more precisely, of majority-rule; i.e. the possibility that the majority may decide that a tyrant should rule. … [T]hat the principle of majority-rule may lead to self contradictions, was first suggested, as far as I know, by Leonard Nelson … I do not think, however, that Nelson … was aware of the fact that analogous arguments can be raised against all the different particular forms of the theory of sovereignty. All these paradoxes can easily be avoided if we frame our political demands [differently] … We demand a government that rules according to the principles of equalitarianism and protectionism; that tolerates all who are prepared to reciprocate, i.e. who are tolerant; that is controlled by, and accountable to, the public. And we may add that some form of majority vote, together with institutions for keeping the public well informed, is the best, though not infallible, means of controlling such a government. (No infallible means exist.) ¹

Popper has captured with complete clarity, the situation in the modern western world, and particularly, in America. Our tolerance of intolerance has brought the country to its knees. The intolerant have manipulated both the law and the society brilliantly, to establish intolerance as a fundamental right, and not as the quality it is — an act that is fundamentally destructive of the society and, eventually, of the country.

The liberty I contend for is more than toleration. The very idea of toleration is despicable; it supposes that some have a pre-eminence above the rest to grant indulgence; whereas all should be equally free, Jews, Turks, Pagans and Christians.

— Baptist minister John Leland (1754-1841)

The maintenance of liberty in a country is dependent on a balanced use of force. As Reinhold Niebuhr noted,

The limitations of the human mind and imagination, the inability of human beings to transcend their own interests sufficiently to envisage the interests of their fellow-men as clearly as they do their own makes force an inevitable part of the process of social cohesion. But the same force which guarantees peace also makes for injustice. ²

Liberty within our society lives in the balance between forcibly restraining the unjust and absolutely permitting toleration at all levels. Modern America has chosen to extend the reach of the unjust, allowing them to deny certain groups their full measure of liberty, by sanctifying the tolerance of intolerance.

It’s not free speech, and not a fundamental right, to call a black man a n*gger. It is intolerance, an action to deprive that black man of his liberty as effectively as throwing him to the ground and putting him in shackles. No black individual — no man, woman, or child — is free, in America, to go anywhere, to take part in American society, without having the threat of, or the actual, limits placed on their activities by the intolerant. After the passage of the Civil Rights Act, my father said to me, “I am in favor of civil rights, but I should not be forced to sell my house to a black man if I don’t want to.” Even at the age of 15, I knew this was ridiculous nonsense. Fifty years later, people still make this same ridiculous statement to me. I no longer extend to them the courtesy of thinking they’re just confused. They’re intolerant, and deliberately baking intolerance into the structure of the society.

If you find that your defense of liberty pits you against the people whose liberty is actually threatened, you’re doing it wrong. If your conception of liberty demands that one group of people be allowed to restrict the liberty of another, through social and economic intolerance, and through violence, you’re doing it wrong. If your conception of liberty leads you to declare that the haves must be protected from the have-nots, and not the other way around, you’re doing it wrong. If you find that your religion blesses intolerance, you’re doing it wrong. If you think that intolerance will make society a better place, by driving away the undesirables, … you’re just wrong.

A country can only be free when its citizens are brave enough to refuse to tolerate intolerance.