"Some statements are both true and dangerous. This is one of them."
The quote above is my standard example. The fact that a true statement can be dangerous provides an argument for suppressing freedom of speech. Which is why that true statement is dangerous.
I am currently on call for jury duty, which reminds me of an example of the same principle which both I and my readers are considerably more likely to face as a real moral choice. We rarely have the opportunity to suppress speech or writing, whether or not we approve of such suppression. But I, like those of my readers who also live in countries under the Anglo-American jury system, may well have to decide whether or not someone accused of a crime will go to jail for it.
The last time I was here, a year or two back, I got as far as the point at which the judge questioned prospective jurors. She asked me whether, if I disagreed with the law the defendant was accused of violating, I would still be willing to vote for conviction if I thought he was guilty. I replied that I would not—and was dismissed from the jury.
In that particular case, it was, for me, a real issue, since the defendant was accused of having carried a concealed handgun. The most visible supporter of laws permitting concealed carry has for many years been John Lott, a friend and ex-student of mine. And, well before he coauthored an empirical piece supporting the claim that concealed carry reduced confrontational crimes, I had sketched the theoretical argument in my Price Theory. If I had remained on the jury and concluded that the defendant was guilty, I would probably have voted for acquittal on the grounds that he did not deserve to be punished for breaking a law that ought not to have existed.
That is an example of jury nullification, the doctrine that jurors should nullify bad laws by voting to acquit those accused of violating them—even if they are guilty.
It is also an example of the "true and dangerous" problem. I do not believe that right and wrong are made by act of Congress or majority vote. Hence I do not believe that it is just to imprison someone for doing something which he has a moral right to do, even if he does not have a legal right to do it. I do not believe that it is morally legitimate for me to participate in violating someone's rights, save perhaps in extreme circumstances (for examples, see other things I have written, especially Chapter 41 of The Machinery of Freedom). It follows not only that I may acquit someone guilty of doing something that ought not to be illegal, I am in most circumstances morally required to.
Suppose everyone accepts the principle. Further suppose that some significant fraction of the population, say 20%, believe that certain people do not have rights, or at least do not have the right to live—gays, blacks, communists, illegal immigrants, whatever. One of them goes around murdering such people. When he is arrested, the odds are high—about .93—that at least one of his fellow believers is on the jury. If the doctrine of juror nullification is widely accepted, that is enough to keep him from being convicted.
Some statements are both true and dangerous. Including this one.