The paradox of tolerance states that if a society is tolerant without limit, its ability to be tolerant is eventually seized or destroyed by the intolerant. Karl Popper described it as the seemingly paradoxical idea that, "In order to maintain a tolerant society, the society must be intolerant of intolerance." The paradox of tolerance is an important concept for thinking about which boundaries can or should be set.
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 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.
In 1971, philosopher John Rawls concluded in A Theory of Justice that a just society must tolerate the intolerant, for otherwise, the society would then itself be intolerant, and thus unjust. However, Rawls also insists, like Popper, that society has a reasonable right of self-preservation against acts of intolerance that supersedes the principle of tolerance: "While an intolerant sect does not itself have title to complain of intolerance, its freedom should be restricted only when the tolerant sincerely and with reason believe that their own security and that of the institutions of liberty are in danger."
In On Toleration (1997), Michael Walzer asked, "Should we tolerate the intolerant?" He claims that most minority religious groups who are the beneficiaries of tolerance are themselves intolerant, at least in some respects. In a tolerant regime, such (intolerant) people may learn to tolerate, or at least to behave "as if they possessed this virtue". Such behavioral modification may be affected, without clearly knowing intentions of such people, by using a forgiving but provocable nice-guy strategy.
Thomas Jefferson had already addressed the notion of a tolerant society in his first inaugural speech, concerning those who might destabilise the United States and its unity, saying, "let them stand undisturbed as monuments of the safety with which error of opinion may be tolerated where reason is left free to combat it."
The paradox of tolerance is important in the discussion of what, if any, boundaries are to be set on freedom of speech. Raphael Cohen-Almagor, in "Popper's Paradox of Tolerance and Its Modification" (1994), asserts that to allow freedom of speech to those who would use it to eliminate the very principle upon which that freedom relies is paradoxical. Michel Rosenfeld, in the Harvard Law Review in 1987, stated: "it seems contradictory to extend freedom of speech to extremists who ... if successful, ruthlessly suppress the speech of those with whom they disagree" and points out that the Western European democracies and the United States have opposite approaches to the question of tolerance of hate speech.
The relation between homophily (a preference for interacting with those with similar traits) and intolerance is manifested when a tolerant person is faced with choosing between either a) a positive relationship with a tolerant individual of a dissimilar out-group, or b) a positive relationship with an intolerant in-group member. In the first case, the out-group relationship is disapproved of by the intolerant in-group member. In the second case, the negative relationship toward the out-group individual is endorsed by the intolerant in-group member. Thus, tolerant group members face being ostracized for their toleration by intolerant members of their in-group, or, in the alternative, being rewarded for demonstrating their out-group intolerance to intolerant members of their in-group.
This dilemma has been considered by Fernando Aguiar and Antonio Parravano in "Tolerating the Intolerant: Homophily, Intolerance, and Segregation in Social Balanced Networks", modeling a community of individuals whose relationships are governed by a modified form of the Heider balance theory.
The means of reaching agreement are repeatedly thrust aside by the instruments of force.