John Stuart Mill is a utilitarian, like Peter Singer and unlike Judith Jarvis Thomson. He thinks that there is a utilitarian case for freedom of thought and expression. That means that he will try to show that never suppressing opinions will do more to promote the greatest overall good than suppressing some opinions would.
Stated in the abstract, Mill’s case seems obvious. To see why it is not, consider some more concrete examples. For example, I wish that no one had racist thoughts, or, at least, that the people who have them did not express them in public. And I also wish that some of the more extreme forms of scepticism about vaccines did not exist, or, at least, that no one was able to spread wild falsehoods about vaccines.
Of course, it is not obvious how anyone would go about this as a practical matter. You cannot order people to believe what you want them to. But you can delete their social media posts, fine media companies that publish their views, teach impressionable children that they are wrong, shun them socially, expel them from schools, fire them from their jobs, or even imprison them. It is not always clear that the costs of doing these things would be worth it. It is extremely difficult to stamp out an idea and the costs of trying can be very high. But these are things you could do.
Still, put all that to one side. If I could wave a wand and make racist beliefs and extreme kinds of vaccine denial simply go away, without cost, I would be sorely tempted to do it.
Mill says that I should not, even if the costs are zero. If he is right, then I should not do the real things I could do either, where the costs are greater than zero.
Mill divides his chapter into two branches. He assumes that there is an opinion that people want to suppress and he says there are two possibilities, either the opinion is true or it is false. He takes up the first possibility on the first branch and the second on the second branch.1
Why would anyone suppress an opinion that they believe is true? I can think of a few reasons. But Mill does not think this is live possibility. Instead, he believes, those favoring suppression will believe that the opinion they wish to suppress is false. So this branch of the argument is really about a narrower question than “should you suppress a true opinion?” It is about whether it is possible to have enough evidence to conclude that an opinion is false and so eligible for suppression.
It seems to me that this is Mill’s core argument on this branch (see paragraph 6).
We are justified in suppressing an opinion only if we are justified in thinking it is false.
We are justified in thinking an opinion is false only if others have “complete liberty of contradicting and disproving” what we think.
Suppressing an opinion denies others the liberty of contradicting and disproving what we think.
Therefore, we cannot be justified in suppressing an opinion. Doing so would be inconsistent with condition 2.
On the second branch, Mill puts aside the condition he argued for on the first branch. Suppose, for the sake of argument, that you are certain that an opinion is false. Mill does not think you can achieve that level of certainty, but he thinks he can still win the argument even if you disagree with him about that.
Mill’s claim on the second branch is that we can only know the truth if we tolerate false opinions. In some moments, he goes beyond tolerance to say that we have to consider and refute false opinions in order to have genuine knowledge; if so, it is not enough to let the false opinions exist out of sight but, rather, you have to think about them. The conclusion is that suppressing false opinions moves a society further from the truth than allowing them to circulate freely does. That is surprising!
However unwillingly a person who has a strong opinion may admit the possibility that his opinion may be false, he ought to be moved by the consideration that however true it may be, if it is not fully, frequently, and fearlessly discussed, it will be held as a dead dogma, not a living truth. (2 ¶21)
Here is how I think Mill’s argument goes
We can know that a statement, S, is the truth only if we understand why the reasons against believing S are false.
We will only consider the reasons against things we believe if they are presented by other people.
Therefore, we will understand the truth only if others have the liberty to express their opinions.
I am especially interested in the argument that I marked as “g” in the text, starting on paragraph 31. Does Mill think that we need to consider what cranks and contrarians think on any given topic in order to have knowledge about that topic?
The two branches of Mill’s argument.
Take an opinion that you loathe. Try to understand what Mill would say about why you should tolerate it, even if you could just make it disappear.