Third, Mill considers the criticism that truth may be justifiably persecuted, because persecution is something that truth should have to face, and it will always survive. Mill replies that such a sentiment is harshly unfair to those who actually are persecuted for holding true ideas. By discovering something true, these people have performed a great service to humanity. Supporting the persecution of such people suggests that their contributions are not truly being valued. Mill also contends that it is wrong to assume that "truth always triumphs over persecution." It may take centuries for truth to reemerge after it is suppressed. For example, Mill writes that the Reformation of the Catholic Church was put down twenty times before Martin Luther was successful. It is mere sentimentality to think that truth is stronger than error, although truth will tend to be rediscovered over time if it is extinguished.
Fourth, Mill responds to the possible argument against him that since we do not actually put dissenters to death any more, no true opinion will ever be extinguished. Mill replies that legal persecution for opinions is still significant in society, for example in the case of blasphemy or atheism. There is also no guarantee, given general public opinion, that more extreme forms of legal persecution will not reemerge. In addition, there continues to be social intolerance of dissent. Mill argues that societal intolerance causes people to hide their views, and stifles intellectualism and independent thought. Stifling free thinking hurts truth, no matter whether a particular instance of free thinking leads to false conclusions.
In Chapter 2, Mill looks exclusively at issues of freedom of thought and of opinion. It is significant that he attempts to justify the importance of this freedom by showing its social benefits--for Mill, diversity of opinion is a positive societal good.
Mill's argument that the dissenting opinion may be true brings up some important points. First, it highlights that Mill believes that moral truths do exist. Thus, in defending liberty, Mill does not say that all opinions are equally valid. Mill is not a relativist; he is not saying that all things can be true according to their circumstances. Rather, he is simply saying that any single idea might be true, and that for this reason no idea can be dismissed, since truth is a boon to progress.
Second, Mill tries to show the contingency of popular beliefs about truth while going to great lengths to not actually state that any popular views about things like religion are wrong. To accomplish this, he observes that in the past people have been persecuted for what is now believed to be true. Thus, Mill creates a logical situation in which anyone reading must accept that if they support persecuting "false" views, then they are required to accept their own persecution if in the minority on a specific issue. Mill is thereby able to dismiss the persecution of "false" views, without condemning modern views as being false.
Third, Mill's examples of persecuted truths reflect some of his rhetorical strategies in this essay. Mill is very conscious of his audience in 19th century England, and he uses examples, like the crucifixion of Christ, which would certainly have resonance with his readers. This reflects a more general strategy in this essay of choosing familiar and often uncontroversial examples in order to make much broader moral claims. In reading this essay it is important to remember that England did not have the same legal protection of liberty that it has today; Mill uses examples to make his points that would not get him into trouble with the law or English society.